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<chapter id="client-authentication">
<title>Client Authentication</title>
<indexterm zone="client-authentication">
<primary>client authentication</primary>
</indexterm>
<para>
When a client application connects to the database server, it
specifies which <productname>PostgreSQL</productname> database user name it
wants to connect as, much the same way one logs into a Unix computer
as a particular user. Within the SQL environment the active database
user name determines access privileges to database objects &mdash; see
<xref linkend="user-manag"/> for more information. Therefore, it is
essential to restrict which database users can connect.
</para>
<note>
<para>
As explained in <xref linkend="user-manag"/>,
<productname>PostgreSQL</productname> actually does privilege
management in terms of <quote>roles</quote>. In this chapter, we
consistently use <firstterm>database user</firstterm> to mean <quote>role with the
<literal>LOGIN</literal> privilege</quote>.
</para>
</note>
<para>
<firstterm>Authentication</firstterm> is the process by which the
database server establishes the identity of the client, and by
extension determines whether the client application (or the user
who runs the client application) is permitted to connect with the
database user name that was requested.
</para>
<para>
<productname>PostgreSQL</productname> offers a number of different
client authentication methods. The method used to authenticate a
particular client connection can be selected on the basis of
(client) host address, database, and user.
</para>
<para>
<productname>PostgreSQL</productname> database user names are logically
separate from user names of the operating system in which the server
runs. If all the users of a particular server also have accounts on
the server's machine, it makes sense to assign database user names
that match their operating system user names. However, a server that
accepts remote connections might have many database users who have no local
operating system
account, and in such cases there need be no connection between
database user names and OS user names.
</para>
<sect1 id="auth-pg-hba-conf">
<title>The <filename>pg_hba.conf</filename> File</title>
<indexterm zone="auth-pg-hba-conf">
<primary>pg_hba.conf</primary>
</indexterm>
<para>
Client authentication is controlled by a configuration file,
which traditionally is named
<filename>pg_hba.conf</filename> and is stored in the database
cluster's data directory.
(<acronym>HBA</acronym> stands for host-based authentication.) A default
<filename>pg_hba.conf</filename> file is installed when the data
directory is initialized by <command>initdb</command>. It is
possible to place the authentication configuration file elsewhere,
however; see the <xref linkend="guc-hba-file"/> configuration parameter.
</para>
<para>
The general format of the <filename>pg_hba.conf</filename> file is
a set of records, one per line. Blank lines are ignored, as is any
text after the <literal>#</literal> comment character.
A record can be continued onto the next line by ending the line with
a backslash. (Backslashes are not special except at the end of a line.)
A record is made
up of a number of fields which are separated by spaces and/or tabs.
Fields can contain white space if the field value is double-quoted.
Quoting one of the keywords in a database, user, or address field (e.g.,
<literal>all</literal> or <literal>replication</literal>) makes the word lose its special
meaning, and just match a database, user, or host with that name.
Backslash line continuation applies even within quoted text or comments.
</para>
<para>
Each record specifies a connection type, a client IP address range
(if relevant for the connection type), a database name, a user name,
and the authentication method to be used for connections matching
these parameters. The first record with a matching connection type,
client address, requested database, and user name is used to perform
authentication. There is no <quote>fall-through</quote> or
<quote>backup</quote>: if one record is chosen and the authentication
fails, subsequent records are not considered. If no record matches,
access is denied.
</para>
<para>
A record can have several formats:
<synopsis>
local <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
host <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>address</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostssl <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>address</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostnossl <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>address</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostgssenc <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>address</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostnogssenc <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>address</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
host <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>IP-address</replaceable> <replaceable>IP-mask</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostssl <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>IP-address</replaceable> <replaceable>IP-mask</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostnossl <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>IP-address</replaceable> <replaceable>IP-mask</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostgssenc <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>IP-address</replaceable> <replaceable>IP-mask</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
hostnogssenc <replaceable>database</replaceable> <replaceable>user</replaceable> <replaceable>IP-address</replaceable> <replaceable>IP-mask</replaceable> <replaceable>auth-method</replaceable> <optional><replaceable>auth-options</replaceable></optional>
</synopsis>
The meaning of the fields is as follows:
<variablelist>
<varlistentry>
<term><literal>local</literal></term>
<listitem>
<para>
This record matches connection attempts using Unix-domain
sockets. Without a record of this type, Unix-domain socket
connections are disallowed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>host</literal></term>
<listitem>
<para>
This record matches connection attempts made using TCP/IP.
<literal>host</literal> records match
<acronym>SSL</acronym> or non-<acronym>SSL</acronym> connection
attempts as well as <acronym>GSSAPI</acronym> encrypted or
non-<acronym>GSSAPI</acronym> encrypted connection attempts.
</para>
<note>
<para>
Remote TCP/IP connections will not be possible unless
the server is started with an appropriate value for the
<xref linkend="guc-listen-addresses"/> configuration parameter,
since the default behavior is to listen for TCP/IP connections
only on the local loopback address <literal>localhost</literal>.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>hostssl</literal></term>
<listitem>
<para>
This record matches connection attempts made using TCP/IP,
but only when the connection is made with <acronym>SSL</acronym>
encryption.
</para>
<para>
To make use of this option the server must be built with
<acronym>SSL</acronym> support. Furthermore,
<acronym>SSL</acronym> must be enabled
by setting the <xref linkend="guc-ssl"/> configuration parameter (see
<xref linkend="ssl-tcp"/> for more information).
Otherwise, the <literal>hostssl</literal> record is ignored except for
logging a warning that it cannot match any connections.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>hostnossl</literal></term>
<listitem>
<para>
This record type has the opposite behavior of <literal>hostssl</literal>;
it only matches connection attempts made over
TCP/IP that do not use <acronym>SSL</acronym>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>hostgssenc</literal></term>
<listitem>
<para>
This record matches connection attempts made using TCP/IP,
but only when the connection is made with <acronym>GSSAPI</acronym>
encryption.
</para>
<para>
To make use of this option the server must be built with
<acronym>GSSAPI</acronym> support. Otherwise,
the <literal>hostgssenc</literal> record is ignored except for logging
a warning that it cannot match any connections.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>hostnogssenc</literal></term>
<listitem>
<para>
This record type has the opposite behavior of <literal>hostgssenc</literal>;
it only matches connection attempts made over
TCP/IP that do not use <acronym>GSSAPI</acronym> encryption.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>database</replaceable></term>
<listitem>
<para>
Specifies which database name(s) this record matches. The value
<literal>all</literal> specifies that it matches all databases.
The value <literal>sameuser</literal> specifies that the record
matches if the requested database has the same name as the
requested user. The value <literal>samerole</literal> specifies that
the requested user must be a member of the role with the same
name as the requested database. (<literal>samegroup</literal> is an
obsolete but still accepted spelling of <literal>samerole</literal>.)
Superusers are not considered to be members of a role for the
purposes of <literal>samerole</literal> unless they are explicitly
members of the role, directly or indirectly, and not just by
virtue of being a superuser.
The value <literal>replication</literal> specifies that the record
matches if a physical replication connection is requested, however, it
doesn't match with logical replication connections. Note that physical
replication connections do not specify any particular database whereas
logical replication connections do specify it.
Otherwise, this is the name of
a specific <productname>PostgreSQL</productname> database.
Multiple database names can be supplied by separating them with
commas. A separate file containing database names can be specified by
preceding the file name with <literal>@</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>user</replaceable></term>
<listitem>
<para>
Specifies which database user name(s) this record
matches. The value <literal>all</literal> specifies that it
matches all users. Otherwise, this is either the name of a specific
database user, or a group name preceded by <literal>+</literal>.
(Recall that there is no real distinction between users and groups
in <productname>PostgreSQL</productname>; a <literal>+</literal> mark really means
<quote>match any of the roles that are directly or indirectly members
of this role</quote>, while a name without a <literal>+</literal> mark matches
only that specific role.) For this purpose, a superuser is only
considered to be a member of a role if they are explicitly a member
of the role, directly or indirectly, and not just by virtue of
being a superuser.
Multiple user names can be supplied by separating them with commas.
A separate file containing user names can be specified by preceding the
file name with <literal>@</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>address</replaceable></term>
<listitem>
<para>
Specifies the client machine address(es) that this record
matches. This field can contain either a host name, an IP
address range, or one of the special key words mentioned below.
</para>
<para>
An IP address range is specified using standard numeric notation
for the range's starting address, then a slash (<literal>/</literal>)
and a <acronym>CIDR</acronym> mask length. The mask
length indicates the number of high-order bits of the client
IP address that must match. Bits to the right of this should
be zero in the given IP address.
There must not be any white space between the IP address, the
<literal>/</literal>, and the CIDR mask length.
</para>
<para>
Typical examples of an IPv4 address range specified this way are
<literal>172.20.143.89/32</literal> for a single host, or
<literal>172.20.143.0/24</literal> for a small network, or
<literal>10.6.0.0/16</literal> for a larger one.
An IPv6 address range might look like <literal>::1/128</literal>
for a single host (in this case the IPv6 loopback address) or
<literal>fe80::7a31:c1ff:0000:0000/96</literal> for a small
network.
<literal>0.0.0.0/0</literal> represents all
IPv4 addresses, and <literal>::0/0</literal> represents
all IPv6 addresses.
To specify a single host, use a mask length of 32 for IPv4 or
128 for IPv6. In a network address, do not omit trailing zeroes.
</para>
<para>
An entry given in IPv4 format will match only IPv4 connections,
and an entry given in IPv6 format will match only IPv6 connections,
even if the represented address is in the IPv4-in-IPv6 range.
Note that entries in IPv6 format will be rejected if the system's
C library does not have support for IPv6 addresses.
</para>
<para>
You can also write <literal>all</literal> to match any IP address,
<literal>samehost</literal> to match any of the server's own IP
addresses, or <literal>samenet</literal> to match any address in any
subnet that the server is directly connected to.
</para>
<para>
If a host name is specified (anything that is not an IP address
range or a special key word is treated as a host name),
that name is compared with the result of a reverse name
resolution of the client's IP address (e.g., reverse DNS
lookup, if DNS is used). Host name comparisons are case
insensitive. If there is a match, then a forward name
resolution (e.g., forward DNS lookup) is performed on the host
name to check whether any of the addresses it resolves to are
equal to the client's IP address. If both directions match,
then the entry is considered to match. (The host name that is
used in <filename>pg_hba.conf</filename> should be the one that
address-to-name resolution of the client's IP address returns,
otherwise the line won't be matched. Some host name databases
allow associating an IP address with multiple host names, but
the operating system will only return one host name when asked
to resolve an IP address.)
</para>
<para>
A host name specification that starts with a dot
(<literal>.</literal>) matches a suffix of the actual host
name. So <literal>.example.com</literal> would match
<literal>foo.example.com</literal> (but not just
<literal>example.com</literal>).
</para>
<para>
When host names are specified
in <filename>pg_hba.conf</filename>, you should make sure that
name resolution is reasonably fast. It can be of advantage to
set up a local name resolution cache such
as <command>nscd</command>. Also, you may wish to enable the
configuration parameter <varname>log_hostname</varname> to see
the client's host name instead of the IP address in the log.
</para>
<para>
These fields do not apply to <literal>local</literal> records.
</para>
<note>
<para>
Users sometimes wonder why host names are handled
in this seemingly complicated way, with two name resolutions
including a reverse lookup of the client's IP address. This
complicates use of the feature in case the client's reverse DNS
entry is not set up or yields some undesirable host name.
It is done primarily for efficiency: this way, a connection attempt
requires at most two resolver lookups, one reverse and one forward.
If there is a resolver problem with some address, it becomes only
that client's problem. A hypothetical alternative
implementation that only did forward lookups would have to
resolve every host name mentioned in
<filename>pg_hba.conf</filename> during every connection attempt.
That could be quite slow if many names are listed.
And if there is a resolver problem with one of the host names,
it becomes everyone's problem.
</para>
<para>
Also, a reverse lookup is necessary to implement the suffix
matching feature, because the actual client host name needs to
be known in order to match it against the pattern.
</para>
<para>
Note that this behavior is consistent with other popular
implementations of host name-based access control, such as the
Apache HTTP Server and TCP Wrappers.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>IP-address</replaceable></term>
<term><replaceable>IP-mask</replaceable></term>
<listitem>
<para>
These two fields can be used as an alternative to the
<replaceable>IP-address</replaceable><literal>/</literal><replaceable>mask-length</replaceable>
notation. Instead of
specifying the mask length, the actual mask is specified in a
separate column. For example, <literal>255.0.0.0</literal> represents an IPv4
CIDR mask length of 8, and <literal>255.255.255.255</literal> represents a
CIDR mask length of 32.
</para>
<para>
These fields do not apply to <literal>local</literal> records.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>auth-method</replaceable></term>
<listitem>
<para>
Specifies the authentication method to use when a connection matches
this record. The possible choices are summarized here; details
are in <xref linkend="auth-methods"/>.
<variablelist>
<varlistentry>
<term><literal>trust</literal></term>
<listitem>
<para>
Allow the connection unconditionally. This method
allows anyone that can connect to the
<productname>PostgreSQL</productname> database server to login as
any <productname>PostgreSQL</productname> user they wish,
without the need for a password or any other authentication. See <xref
linkend="auth-trust"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>reject</literal></term>
<listitem>
<para>
Reject the connection unconditionally. This is useful for
<quote>filtering out</quote> certain hosts from a group, for example a
<literal>reject</literal> line could block a specific host from connecting,
while a later line allows the remaining hosts in a specific
network to connect.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>scram-sha-256</literal></term>
<listitem>
<para>
Perform SCRAM-SHA-256 authentication to verify the user's
password. See <xref linkend="auth-password"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>md5</literal></term>
<listitem>
<para>
Perform SCRAM-SHA-256 or MD5 authentication to verify the
user's password. See <xref linkend="auth-password"/>
for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>password</literal></term>
<listitem>
<para>
Require the client to supply an unencrypted password for
authentication.
Since the password is sent in clear text over the
network, this should not be used on untrusted networks.
See <xref linkend="auth-password"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>gss</literal></term>
<listitem>
<para>
Use GSSAPI to authenticate the user. This is only
available for TCP/IP connections. See <xref
linkend="gssapi-auth"/> for details. It can be used in conjunction
with GSSAPI encryption.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>sspi</literal></term>
<listitem>
<para>
Use SSPI to authenticate the user. This is only
available on Windows. See <xref
linkend="sspi-auth"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ident</literal></term>
<listitem>
<para>
Obtain the operating system user name of the client
by contacting the ident server on the client
and check if it matches the requested database user name.
Ident authentication can only be used on TCP/IP
connections. When specified for local connections, peer
authentication will be used instead.
See <xref linkend="auth-ident"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>peer</literal></term>
<listitem>
<para>
Obtain the client's operating system user name from the operating
system and check if it matches the requested database user name.
This is only available for local connections.
See <xref linkend="auth-peer"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldap</literal></term>
<listitem>
<para>
Authenticate using an <acronym>LDAP</acronym> server. See <xref
linkend="auth-ldap"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>radius</literal></term>
<listitem>
<para>
Authenticate using a RADIUS server. See <xref
linkend="auth-radius"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>cert</literal></term>
<listitem>
<para>
Authenticate using SSL client certificates. See
<xref linkend="auth-cert"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>pam</literal></term>
<listitem>
<para>
Authenticate using the Pluggable Authentication Modules
(PAM) service provided by the operating system. See <xref
linkend="auth-pam"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>bsd</literal></term>
<listitem>
<para>
Authenticate using the BSD Authentication service provided by the
operating system. See <xref linkend="auth-bsd"/> for details.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>auth-options</replaceable></term>
<listitem>
<para>
After the <replaceable>auth-method</replaceable> field, there can be field(s) of
the form <replaceable>name</replaceable><literal>=</literal><replaceable>value</replaceable> that
specify options for the authentication method. Details about which
options are available for which authentication methods appear below.
</para>
<para>
In addition to the method-specific options listed below, there is a
method-independent authentication option <literal>clientcert</literal>, which
can be specified in any <literal>hostssl</literal> record.
This option can be set to <literal>verify-ca</literal> or
<literal>verify-full</literal>. Both options require the client
to present a valid (trusted) SSL certificate, while
<literal>verify-full</literal> additionally enforces that the
<literal>cn</literal> (Common Name) in the certificate matches
the username or an applicable mapping.
This behavior is similar to the <literal>cert</literal> authentication
method (see <xref linkend="auth-cert"/>) but enables pairing
the verification of client certificates with any authentication
method that supports <literal>hostssl</literal> entries.
</para>
<para>
On any record using client certificate authentication (i.e. one
using the <literal>cert</literal> authentication method or one
using the <literal>clientcert</literal> option), you can specify
which part of the client certificate credentials to match using
the <literal>clientname</literal> option. This option can have one
of two values. If you specify <literal>clientname=CN</literal>, which
is the default, the username is matched against the certificate's
<literal>Common Name (CN)</literal>. If instead you specify
<literal>clientname=DN</literal> the username is matched against the
entire <literal>Distinguished Name (DN)</literal> of the certificate.
This option is probably best used in conjunction with a username map.
The comparison is done with the <literal>DN</literal> in
<ulink url="https://tools.ietf.org/html/rfc2253">RFC 2253</ulink>
format. To see the <literal>DN</literal> of a client certificate
in this format, do
<programlisting>
openssl x509 -in myclient.crt -noout --subject -nameopt RFC2253 | sed "s/^subject=//"
</programlisting>
Care needs to be taken when using this option, especially when using
regular expression matching against the <literal>DN</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
Files included by <literal>@</literal> constructs are read as lists of names,
which can be separated by either whitespace or commas. Comments are
introduced by <literal>#</literal>, just as in
<filename>pg_hba.conf</filename>, and nested <literal>@</literal> constructs are
allowed. Unless the file name following <literal>@</literal> is an absolute
path, it is taken to be relative to the directory containing the
referencing file.
</para>
<para>
Since the <filename>pg_hba.conf</filename> records are examined
sequentially for each connection attempt, the order of the records is
significant. Typically, earlier records will have tight connection
match parameters and weaker authentication methods, while later
records will have looser match parameters and stronger authentication
methods. For example, one might wish to use <literal>trust</literal>
authentication for local TCP/IP connections but require a password for
remote TCP/IP connections. In this case a record specifying
<literal>trust</literal> authentication for connections from 127.0.0.1 would
appear before a record specifying password authentication for a wider
range of allowed client IP addresses.
</para>
<para>
The <filename>pg_hba.conf</filename> file is read on start-up and when
the main server process receives a
<systemitem>SIGHUP</systemitem><indexterm><primary>SIGHUP</primary></indexterm>
signal. If you edit the file on an
active system, you will need to signal the postmaster
(using <literal>pg_ctl reload</literal>, calling the SQL function
<function>pg_reload_conf()</function>, or using <literal>kill
-HUP</literal>) to make it re-read the file.
</para>
<note>
<para>
The preceding statement is not true on Microsoft Windows: there, any
changes in the <filename>pg_hba.conf</filename> file are immediately
applied by subsequent new connections.
</para>
</note>
<para>
The system view
<link linkend="view-pg-hba-file-rules"><structname>pg_hba_file_rules</structname></link>
can be helpful for pre-testing changes to the <filename>pg_hba.conf</filename>
file, or for diagnosing problems if loading of the file did not have the
desired effects. Rows in the view with
non-null <structfield>error</structfield> fields indicate problems in the
corresponding lines of the file.
</para>
<tip>
<para>
To connect to a particular database, a user must not only pass the
<filename>pg_hba.conf</filename> checks, but must have the
<literal>CONNECT</literal> privilege for the database. If you wish to
restrict which users can connect to which databases, it's usually
easier to control this by granting/revoking <literal>CONNECT</literal> privilege
than to put the rules in <filename>pg_hba.conf</filename> entries.
</para>
</tip>
<para>
Some examples of <filename>pg_hba.conf</filename> entries are shown in
<xref linkend="example-pg-hba.conf"/>. See the next section for details on the
different authentication methods.
</para>
<example id="example-pg-hba.conf">
<title>Example <filename>pg_hba.conf</filename> Entries</title>
<programlisting>
# Allow any user on the local system to connect to any database with
# any database user name using Unix-domain sockets (the default for local
# connections).
#
# TYPE DATABASE USER ADDRESS METHOD
local all all trust
# The same using local loopback TCP/IP connections.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all 127.0.0.1/32 trust
# The same as the previous line, but using a separate netmask column
#
# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
host all all 127.0.0.1 255.255.255.255 trust
# The same over IPv6.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all ::1/128 trust
# The same using a host name (would typically cover both IPv4 and IPv6).
#
# TYPE DATABASE USER ADDRESS METHOD
host all all localhost trust
# Allow any user from any host with IP address 192.168.93.x to connect
# to database "postgres" as the same user name that ident reports for
# the connection (typically the operating system user name).
#
# TYPE DATABASE USER ADDRESS METHOD
host postgres all 192.168.93.0/24 ident
# Allow any user from host 192.168.12.10 to connect to database
# "postgres" if the user's password is correctly supplied.
#
# TYPE DATABASE USER ADDRESS METHOD
host postgres all 192.168.12.10/32 scram-sha-256
# Allow any user from hosts in the example.com domain to connect to
# any database if the user's password is correctly supplied.
#
# Require SCRAM authentication for most users, but make an exception
# for user 'mike', who uses an older client that doesn't support SCRAM
# authentication.
#
# TYPE DATABASE USER ADDRESS METHOD
host all mike .example.com md5
host all all .example.com scram-sha-256
# In the absence of preceding "host" lines, these three lines will
# reject all connections from 192.168.54.1 (since that entry will be
# matched first), but allow GSSAPI-encrypted connections from anywhere else
# on the Internet. The zero mask causes no bits of the host IP address to
# be considered, so it matches any host. Unencrypted GSSAPI connections
# (which "fall through" to the third line since "hostgssenc" only matches
# encrypted GSSAPI connections) are allowed, but only from 192.168.12.10.
#
# TYPE DATABASE USER ADDRESS METHOD
host all all 192.168.54.1/32 reject
hostgssenc all all 0.0.0.0/0 gss
host all all 192.168.12.10/32 gss
# Allow users from 192.168.x.x hosts to connect to any database, if
# they pass the ident check. If, for example, ident says the user is
# "bryanh" and he requests to connect as PostgreSQL user "guest1", the
# connection is allowed if there is an entry in pg_ident.conf for map
# "omicron" that says "bryanh" is allowed to connect as "guest1".
#
# TYPE DATABASE USER ADDRESS METHOD
host all all 192.168.0.0/16 ident map=omicron
# If these are the only three lines for local connections, they will
# allow local users to connect only to their own databases (databases
# with the same name as their database user name) except for administrators
# and members of role "support", who can connect to all databases. The file
# $PGDATA/admins contains a list of names of administrators. Passwords
# are required in all cases.
#
# TYPE DATABASE USER ADDRESS METHOD
local sameuser all md5
local all @admins md5
local all +support md5
# The last two lines above can be combined into a single line:
local all @admins,+support md5
# The database column can also use lists and file names:
local db1,db2,@demodbs all md5
</programlisting>
</example>
</sect1>
<sect1 id="auth-username-maps">
<title>User Name Maps</title>
<indexterm zone="auth-username-maps">
<primary>User name maps</primary>
</indexterm>
<para>
When using an external authentication system such as Ident or GSSAPI,
the name of the operating system user that initiated the connection
might not be the same as the database user (role) that is to be used.
In this case, a user name map can be applied to map the operating system
user name to a database user. To use user name mapping, specify
<literal>map</literal>=<replaceable>map-name</replaceable>
in the options field in <filename>pg_hba.conf</filename>. This option is
supported for all authentication methods that receive external user names.
Since different mappings might be needed for different connections,
the name of the map to be used is specified in the
<replaceable>map-name</replaceable> parameter in <filename>pg_hba.conf</filename>
to indicate which map to use for each individual connection.
</para>
<para>
User name maps are defined in the ident map file, which by default is named
<filename>pg_ident.conf</filename><indexterm><primary>pg_ident.conf</primary></indexterm>
and is stored in the
cluster's data directory. (It is possible to place the map file
elsewhere, however; see the <xref linkend="guc-ident-file"/>
configuration parameter.)
The ident map file contains lines of the general form:
<synopsis>
<replaceable>map-name</replaceable> <replaceable>system-username</replaceable> <replaceable>database-username</replaceable>
</synopsis>
Comments, whitespace and line continuations are handled in the same way as in
<filename>pg_hba.conf</filename>. The
<replaceable>map-name</replaceable> is an arbitrary name that will be used to
refer to this mapping in <filename>pg_hba.conf</filename>. The other
two fields specify an operating system user name and a matching
database user name. The same <replaceable>map-name</replaceable> can be
used repeatedly to specify multiple user-mappings within a single map.
</para>
<para>
There is no restriction regarding how many database users a given
operating system user can correspond to, nor vice versa. Thus, entries
in a map should be thought of as meaning <quote>this operating system
user is allowed to connect as this database user</quote>, rather than
implying that they are equivalent. The connection will be allowed if
there is any map entry that pairs the user name obtained from the
external authentication system with the database user name that the
user has requested to connect as.
</para>
<para>
If the <replaceable>system-username</replaceable> field starts with a slash (<literal>/</literal>),
the remainder of the field is treated as a regular expression.
(See <xref linkend="posix-syntax-details"/> for details of
<productname>PostgreSQL</productname>'s regular expression syntax.) The regular
expression can include a single capture, or parenthesized subexpression,
which can then be referenced in the <replaceable>database-username</replaceable>
field as <literal>\1</literal> (backslash-one). This allows the mapping of
multiple user names in a single line, which is particularly useful for
simple syntax substitutions. For example, these entries
<programlisting>
mymap /^(.*)@mydomain\.com$ \1
mymap /^(.*)@otherdomain\.com$ guest
</programlisting>
will remove the domain part for users with system user names that end with
<literal>@mydomain.com</literal>, and allow any user whose system name ends with
<literal>@otherdomain.com</literal> to log in as <literal>guest</literal>.
</para>
<tip>
<para>
Keep in mind that by default, a regular expression can match just part of
a string. It's usually wise to use <literal>^</literal> and <literal>$</literal>, as
shown in the above example, to force the match to be to the entire
system user name.
</para>
</tip>
<para>
The <filename>pg_ident.conf</filename> file is read on start-up and
when the main server process receives a
<systemitem>SIGHUP</systemitem><indexterm><primary>SIGHUP</primary></indexterm>
signal. If you edit the file on an
active system, you will need to signal the postmaster
(using <literal>pg_ctl reload</literal>, calling the SQL function
<function>pg_reload_conf()</function>, or using <literal>kill
-HUP</literal>) to make it re-read the file.
</para>
<para>
A <filename>pg_ident.conf</filename> file that could be used in
conjunction with the <filename>pg_hba.conf</filename> file in <xref
linkend="example-pg-hba.conf"/> is shown in <xref
linkend="example-pg-ident.conf"/>. In this example, anyone
logged in to a machine on the 192.168 network that does not have the
operating system user name <literal>bryanh</literal>, <literal>ann</literal>, or
<literal>robert</literal> would not be granted access. Unix user
<literal>robert</literal> would only be allowed access when he tries to
connect as <productname>PostgreSQL</productname> user <literal>bob</literal>, not
as <literal>robert</literal> or anyone else. <literal>ann</literal> would
only be allowed to connect as <literal>ann</literal>. User
<literal>bryanh</literal> would be allowed to connect as either
<literal>bryanh</literal> or as <literal>guest1</literal>.
</para>
<example id="example-pg-ident.conf">
<title>An Example <filename>pg_ident.conf</filename> File</title>
<programlisting>
# MAPNAME SYSTEM-USERNAME PG-USERNAME
omicron bryanh bryanh
omicron ann ann
# bob has user name robert on these machines
omicron robert bob
# bryanh can also connect as guest1
omicron bryanh guest1
</programlisting>
</example>
</sect1>
<sect1 id="auth-methods">
<title>Authentication Methods</title>
<para>
<productname>PostgreSQL</productname> provides various methods for
authenticating users:
<itemizedlist>
<listitem>
<para>
<link linkend="auth-trust">Trust authentication</link>, which
simply trusts that users are who they say they are.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-password">Password authentication</link>, which
requires that users send a password.
</para>
</listitem>
<listitem>
<para>
<link linkend="gssapi-auth">GSSAPI authentication</link>, which
relies on a GSSAPI-compatible security library. Typically this is
used to access an authentication server such as a Kerberos or
Microsoft Active Directory server.
</para>
</listitem>
<listitem>
<para>
<link linkend="sspi-auth">SSPI authentication</link>, which
uses a Windows-specific protocol similar to GSSAPI.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-ident">Ident authentication</link>, which
relies on an <quote>Identification Protocol</quote>
(<ulink url="https://tools.ietf.org/html/rfc1413">RFC 1413</ulink>)
service on the client's machine. (On local Unix-socket connections,
this is treated as peer authentication.)
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-peer">Peer authentication</link>, which
relies on operating system facilities to identify the process at the
other end of a local connection. This is not supported for remote
connections.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-ldap">LDAP authentication</link>, which
relies on an LDAP authentication server.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-radius">RADIUS authentication</link>, which
relies on a RADIUS authentication server.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-cert">Certificate authentication</link>, which
requires an SSL connection and authenticates users by checking the
SSL certificate they send.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-pam">PAM authentication</link>, which
relies on a PAM (Pluggable Authentication Modules) library.
</para>
</listitem>
<listitem>
<para>
<link linkend="auth-bsd">BSD authentication</link>, which
relies on the BSD Authentication framework (currently available
only on OpenBSD).
</para>
</listitem>
</itemizedlist>
</para>
<para>
Peer authentication is usually recommendable for local connections,
though trust authentication might be sufficient in some circumstances.
Password authentication is the easiest choice for remote connections.
All the other options require some kind of external security
infrastructure (usually an authentication server or a certificate
authority for issuing SSL certificates), or are platform-specific.
</para>
<para>
The following sections describe each of these authentication methods
in more detail.
</para>
</sect1>
<sect1 id="auth-trust">
<title>Trust Authentication</title>
<para>
When <literal>trust</literal> authentication is specified,
<productname>PostgreSQL</productname> assumes that anyone who can
connect to the server is authorized to access the database with
whatever database user name they specify (even superuser names).
Of course, restrictions made in the <literal>database</literal> and
<literal>user</literal> columns still apply.
This method should only be used when there is adequate
operating-system-level protection on connections to the server.
</para>
<para>
<literal>trust</literal> authentication is appropriate and very
convenient for local connections on a single-user workstation. It
is usually <emphasis>not</emphasis> appropriate by itself on a multiuser
machine. However, you might be able to use <literal>trust</literal> even
on a multiuser machine, if you restrict access to the server's
Unix-domain socket file using file-system permissions. To do this, set the
<varname>unix_socket_permissions</varname> (and possibly
<varname>unix_socket_group</varname>) configuration parameters as
described in <xref linkend="runtime-config-connection"/>. Or you
could set the <varname>unix_socket_directories</varname>
configuration parameter to place the socket file in a suitably
restricted directory.
</para>
<para>
Setting file-system permissions only helps for Unix-socket connections.
Local TCP/IP connections are not restricted by file-system permissions.
Therefore, if you want to use file-system permissions for local security,
remove the <literal>host ... 127.0.0.1 ...</literal> line from
<filename>pg_hba.conf</filename>, or change it to a
non-<literal>trust</literal> authentication method.
</para>
<para>
<literal>trust</literal> authentication is only suitable for TCP/IP connections
if you trust every user on every machine that is allowed to connect
to the server by the <filename>pg_hba.conf</filename> lines that specify
<literal>trust</literal>. It is seldom reasonable to use <literal>trust</literal>
for any TCP/IP connections other than those from <systemitem>localhost</systemitem> (127.0.0.1).
</para>
</sect1>
<sect1 id="auth-password">
<title>Password Authentication</title>
<indexterm>
<primary>MD5</primary>
</indexterm>
<indexterm>
<primary>SCRAM</primary>
</indexterm>
<indexterm>
<primary>password</primary>
<secondary>authentication</secondary>
</indexterm>
<para>
There are several password-based authentication methods. These methods
operate similarly but differ in how the users' passwords are stored on the
server and how the password provided by a client is sent across the
connection.
</para>
<variablelist>
<varlistentry>
<term><literal>scram-sha-256</literal></term>
<listitem>
<para>
The method <literal>scram-sha-256</literal> performs SCRAM-SHA-256
authentication, as described in
<ulink url="https://tools.ietf.org/html/rfc7677">RFC 7677</ulink>. It
is a challenge-response scheme that prevents password sniffing on
untrusted connections and supports storing passwords on the server in a
cryptographically hashed form that is thought to be secure.
</para>
<para>
This is the most secure of the currently provided methods, but it is
not supported by older client libraries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>md5</literal></term>
<listitem>
<para>
The method <literal>md5</literal> uses a custom less secure challenge-response
mechanism. It prevents password sniffing and avoids storing passwords
on the server in plain text but provides no protection if an attacker
manages to steal the password hash from the server. Also, the MD5 hash
algorithm is nowadays no longer considered secure against determined
attacks.
</para>
<para>
The <literal>md5</literal> method cannot be used with
the <xref linkend="guc-db-user-namespace"/> feature.
</para>
<para>
To ease transition from the <literal>md5</literal> method to the newer
SCRAM method, if <literal>md5</literal> is specified as a method
in <filename>pg_hba.conf</filename> but the user's password on the
server is encrypted for SCRAM (see below), then SCRAM-based
authentication will automatically be chosen instead.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>password</literal></term>
<listitem>
<para>
The method <literal>password</literal> sends the password in clear-text and is
therefore vulnerable to password <quote>sniffing</quote> attacks. It should
always be avoided if possible. If the connection is protected by SSL
encryption then <literal>password</literal> can be used safely, though.
(Though SSL certificate authentication might be a better choice if one
is depending on using SSL).
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
<productname>PostgreSQL</productname> database passwords are
separate from operating system user passwords. The password for
each database user is stored in the <literal>pg_authid</literal> system
catalog. Passwords can be managed with the SQL commands
<xref linkend="sql-createrole"/> and
<xref linkend="sql-alterrole"/>,
e.g., <userinput>CREATE ROLE foo WITH LOGIN PASSWORD 'secret'</userinput>,
or the <application>psql</application>
command <literal>\password</literal>.
If no password has been set up for a user, the stored password
is null and password authentication will always fail for that user.
</para>
<para>
The availability of the different password-based authentication methods
depends on how a user's password on the server is encrypted (or hashed,
more accurately). This is controlled by the configuration
parameter <xref linkend="guc-password-encryption"/> at the time the
password is set. If a password was encrypted using
the <literal>scram-sha-256</literal> setting, then it can be used for the
authentication methods <literal>scram-sha-256</literal>
and <literal>password</literal> (but password transmission will be in
plain text in the latter case). The authentication method
specification <literal>md5</literal> will automatically switch to using
the <literal>scram-sha-256</literal> method in this case, as explained
above, so it will also work. If a password was encrypted using
the <literal>md5</literal> setting, then it can be used only for
the <literal>md5</literal> and <literal>password</literal> authentication
method specifications (again, with the password transmitted in plain text
in the latter case). (Previous PostgreSQL releases supported storing the
password on the server in plain text. This is no longer possible.) To
check the currently stored password hashes, see the system
catalog <literal>pg_authid</literal>.
</para>
<para>
To upgrade an existing installation from <literal>md5</literal>
to <literal>scram-sha-256</literal>, after having ensured that all client
libraries in use are new enough to support SCRAM,
set <literal>password_encryption = 'scram-sha-256'</literal>
in <filename>postgresql.conf</filename>, make all users set new passwords,
and change the authentication method specifications
in <filename>pg_hba.conf</filename> to <literal>scram-sha-256</literal>.
</para>
</sect1>
<sect1 id="gssapi-auth">
<title>GSSAPI Authentication</title>
<indexterm zone="gssapi-auth">
<primary>GSSAPI</primary>
</indexterm>
<para>
<productname>GSSAPI</productname> is an industry-standard protocol
for secure authentication defined in
<ulink url="https://tools.ietf.org/html/rfc2743">RFC 2743</ulink>.
<productname>PostgreSQL</productname>
supports <productname>GSSAPI</productname> for authentication,
communications encryption, or both.
<productname>GSSAPI</productname> provides automatic authentication
(single sign-on) for systems that support it. The authentication itself is
secure. If <productname>GSSAPI</productname> encryption
or <acronym>SSL</acronym> encryption is
used, the data sent along the database connection will be encrypted;
otherwise, it will not.
</para>
<para>
GSSAPI support has to be enabled when <productname>PostgreSQL</productname> is built;
see <xref linkend="installation"/> for more information.
</para>
<para>
When <productname>GSSAPI</productname> uses
<productname>Kerberos</productname>, it uses a standard service
principal (authentication identity) name in the format
<literal><replaceable>servicename</replaceable>/<replaceable>hostname</replaceable>@<replaceable>realm</replaceable></literal>.
The principal name used by a particular installation is not encoded in
the <productname>PostgreSQL</productname> server in any way; rather it
is specified in the <firstterm>keytab</firstterm> file that the server
reads to determine its identity. If multiple principals are listed in
the keytab file, the server will accept any one of them.
The server's realm name is the preferred realm specified in the Kerberos
configuration file(s) accessible to the server.
</para>
<para>
When connecting, the client must know the principal name of the server
it intends to connect to. The <replaceable>servicename</replaceable>
part of the principal is ordinarily <literal>postgres</literal>,
but another value can be selected via <application>libpq</application>'s
<xref linkend="libpq-connect-krbsrvname"/> connection parameter.
The <replaceable>hostname</replaceable> part is the fully qualified
host name that <application>libpq</application> is told to connect to.
The realm name is the preferred realm specified in the Kerberos
configuration file(s) accessible to the client.
</para>
<para>
The client will also have a principal name for its own identity
(and it must have a valid ticket for this principal). To
use <productname>GSSAPI</productname> for authentication, the client
principal must be associated with
a <productname>PostgreSQL</productname> database user name.
The <filename>pg_ident.conf</filename> configuration file can be used
to map principals to user names; for example,
<literal>pgusername@realm</literal> could be mapped to just <literal>pgusername</literal>.
Alternatively, you can use the full <literal>username@realm</literal> principal as
the role name in <productname>PostgreSQL</productname> without any mapping.
</para>
<para>
<productname>PostgreSQL</productname> also supports mapping
client principals to user names by just stripping the realm from
the principal. This method is supported for backwards compatibility and is
strongly discouraged as it is then impossible to distinguish different users
with the same user name but coming from different realms. To enable this,
set <literal>include_realm</literal> to 0. For simple single-realm
installations, doing that combined with setting the
<literal>krb_realm</literal> parameter (which checks that the principal's realm
matches exactly what is in the <literal>krb_realm</literal> parameter)
is still secure; but this is a
less capable approach compared to specifying an explicit mapping in
<filename>pg_ident.conf</filename>.
</para>
<para>
The location of the server's keytab file is specified by the <xref
linkend="guc-krb-server-keyfile"/> configuration parameter.
For security reasons, it is recommended to use a separate keytab
just for the <productname>PostgreSQL</productname> server rather
than allowing the server to read the system keytab file.
Make sure that your server keytab file is readable (and preferably
only readable, not writable) by the <productname>PostgreSQL</productname>
server account. (See also <xref linkend="postgres-user"/>.)
</para>
<para>
The keytab file is generated using the Kerberos software; see the
Kerberos documentation for details. The following example shows
doing this using the <application>kadmin</application> tool of
MIT-compatible Kerberos 5 implementations:
<screen>
<prompt>kadmin% </prompt><userinput>addprinc -randkey postgres/server.my.domain.org</userinput>
<prompt>kadmin% </prompt><userinput>ktadd -k krb5.keytab postgres/server.my.domain.org</userinput>
</screen>
</para>
<para>
The following authentication options are supported for
the <productname>GSSAPI</productname> authentication method:
<variablelist>
<varlistentry>
<term><literal>include_realm</literal></term>
<listitem>
<para>
If set to 0, the realm name from the authenticated user principal is
stripped off before being passed through the user name mapping
(<xref linkend="auth-username-maps"/>). This is discouraged and is
primarily available for backwards compatibility, as it is not secure
in multi-realm environments unless <literal>krb_realm</literal> is
also used. It is recommended to
leave <literal>include_realm</literal> set to the default (1) and to
provide an explicit mapping in <filename>pg_ident.conf</filename> to convert
principal names to <productname>PostgreSQL</productname> user names.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>map</literal></term>
<listitem>
<para>
Allows mapping from client principals to database user names. See
<xref linkend="auth-username-maps"/> for details. For a GSSAPI/Kerberos
principal, such as <literal>username@EXAMPLE.COM</literal> (or, less
commonly, <literal>username/hostbased@EXAMPLE.COM</literal>), the
user name used for mapping is
<literal>username@EXAMPLE.COM</literal> (or
<literal>username/hostbased@EXAMPLE.COM</literal>, respectively),
unless <literal>include_realm</literal> has been set to 0, in which case
<literal>username</literal> (or <literal>username/hostbased</literal>)
is what is seen as the system user name when mapping.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>krb_realm</literal></term>
<listitem>
<para>
Sets the realm to match user principal names against. If this parameter
is set, only users of that realm will be accepted. If it is not set,
users of any realm can connect, subject to whatever user name mapping
is done.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
In addition to these settings, which can be different for
different <filename>pg_hba.conf</filename> entries, there is the
server-wide <xref linkend="guc-krb-caseins-users"/> configuration
parameter. If that is set to true, client principals are matched to
user map entries case-insensitively. <literal>krb_realm</literal>, if
set, is also matched case-insensitively.
</para>
</sect1>
<sect1 id="sspi-auth">
<title>SSPI Authentication</title>
<indexterm zone="sspi-auth">
<primary>SSPI</primary>
</indexterm>
<para>
<productname>SSPI</productname> is a <productname>Windows</productname>
technology for secure authentication with single sign-on.
<productname>PostgreSQL</productname> will use SSPI in
<literal>negotiate</literal> mode, which will use
<productname>Kerberos</productname> when possible and automatically
fall back to <productname>NTLM</productname> in other cases.
<productname>SSPI</productname> authentication only works when both
server and client are running <productname>Windows</productname>,
or, on non-Windows platforms, when <productname>GSSAPI</productname>
is available.
</para>
<para>
When using <productname>Kerberos</productname> authentication,
<productname>SSPI</productname> works the same way
<productname>GSSAPI</productname> does; see <xref linkend="gssapi-auth"/>
for details.
</para>
<para>
The following configuration options are supported for <productname>SSPI</productname>:
<variablelist>
<varlistentry>
<term><literal>include_realm</literal></term>
<listitem>
<para>
If set to 0, the realm name from the authenticated user principal is
stripped off before being passed through the user name mapping
(<xref linkend="auth-username-maps"/>). This is discouraged and is
primarily available for backwards compatibility, as it is not secure
in multi-realm environments unless <literal>krb_realm</literal> is
also used. It is recommended to
leave <literal>include_realm</literal> set to the default (1) and to
provide an explicit mapping in <filename>pg_ident.conf</filename> to convert
principal names to <productname>PostgreSQL</productname> user names.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>compat_realm</literal></term>
<listitem>
<para>
If set to 1, the domain's SAM-compatible name (also known as the
NetBIOS name) is used for the <literal>include_realm</literal>
option. This is the default. If set to 0, the true realm name from
the Kerberos user principal name is used.
</para>
<para>
Do not disable this option unless your server runs under a domain
account (this includes virtual service accounts on a domain member
system) and all clients authenticating through SSPI are also using
domain accounts, or authentication will fail.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>upn_username</literal></term>
<listitem>
<para>
If this option is enabled along with <literal>compat_realm</literal>,
the user name from the Kerberos UPN is used for authentication. If
it is disabled (the default), the SAM-compatible user name is used.
By default, these two names are identical for new user accounts.
</para>
<para>
Note that <application>libpq</application> uses the SAM-compatible name if no
explicit user name is specified. If you use
<application>libpq</application> or a driver based on it, you should
leave this option disabled or explicitly specify user name in the
connection string.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>map</literal></term>
<listitem>
<para>
Allows for mapping between system and database user names. See
<xref linkend="auth-username-maps"/> for details. For an SSPI/Kerberos
principal, such as <literal>username@EXAMPLE.COM</literal> (or, less
commonly, <literal>username/hostbased@EXAMPLE.COM</literal>), the
user name used for mapping is
<literal>username@EXAMPLE.COM</literal> (or
<literal>username/hostbased@EXAMPLE.COM</literal>, respectively),
unless <literal>include_realm</literal> has been set to 0, in which case
<literal>username</literal> (or <literal>username/hostbased</literal>)
is what is seen as the system user name when mapping.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>krb_realm</literal></term>
<listitem>
<para>
Sets the realm to match user principal names against. If this parameter
is set, only users of that realm will be accepted. If it is not set,
users of any realm can connect, subject to whatever user name mapping
is done.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</sect1>
<sect1 id="auth-ident">
<title>Ident Authentication</title>
<indexterm>
<primary>ident</primary>
</indexterm>
<para>
The ident authentication method works by obtaining the client's
operating system user name from an ident server and using it as
the allowed database user name (with an optional user name mapping).
This is only supported on TCP/IP connections.
</para>
<note>
<para>
When ident is specified for a local (non-TCP/IP) connection,
peer authentication (see <xref linkend="auth-peer"/>) will be
used instead.
</para>
</note>
<para>
The following configuration options are supported for <productname>ident</productname>:
<variablelist>
<varlistentry>
<term><literal>map</literal></term>
<listitem>
<para>
Allows for mapping between system and database user names. See
<xref linkend="auth-username-maps"/> for details.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The <quote>Identification Protocol</quote> is described in
<ulink url="https://tools.ietf.org/html/rfc1413">RFC 1413</ulink>.
Virtually every Unix-like
operating system ships with an ident server that listens on TCP
port 113 by default. The basic functionality of an ident server
is to answer questions like <quote>What user initiated the
connection that goes out of your port <replaceable>X</replaceable>
and connects to my port <replaceable>Y</replaceable>?</quote>.
Since <productname>PostgreSQL</productname> knows both <replaceable>X</replaceable> and
<replaceable>Y</replaceable> when a physical connection is established, it
can interrogate the ident server on the host of the connecting
client and can theoretically determine the operating system user
for any given connection.
</para>
<para>
The drawback of this procedure is that it depends on the integrity
of the client: if the client machine is untrusted or compromised,
an attacker could run just about any program on port 113 and
return any user name they choose. This authentication method is
therefore only appropriate for closed networks where each client
machine is under tight control and where the database and system
administrators operate in close contact. In other words, you must
trust the machine running the ident server.
Heed the warning:
<blockquote>
<attribution>RFC 1413</attribution>
<para>
The Identification Protocol is not intended as an authorization
or access control protocol.
</para>
</blockquote>
</para>
<para>
Some ident servers have a nonstandard option that causes the returned
user name to be encrypted, using a key that only the originating
machine's administrator knows. This option <emphasis>must not</emphasis> be
used when using the ident server with <productname>PostgreSQL</productname>,
since <productname>PostgreSQL</productname> does not have any way to decrypt the
returned string to determine the actual user name.
</para>
</sect1>
<sect1 id="auth-peer">
<title>Peer Authentication</title>
<indexterm>
<primary>peer</primary>
</indexterm>
<para>
The peer authentication method works by obtaining the client's
operating system user name from the kernel and using it as the
allowed database user name (with optional user name mapping). This
method is only supported on local connections.
</para>
<para>
The following configuration options are supported for <productname>peer</productname>:
<variablelist>
<varlistentry>
<term><literal>map</literal></term>
<listitem>
<para>
Allows for mapping between system and database user names. See
<xref linkend="auth-username-maps"/> for details.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
Peer authentication is only available on operating systems providing
the <function>getpeereid()</function> function, the <symbol>SO_PEERCRED</symbol>
socket parameter, or similar mechanisms. Currently that includes
<systemitem class="osname">Linux</systemitem>,
most flavors of <systemitem class="osname">BSD</systemitem> including
<systemitem class="osname">macOS</systemitem>,
and <systemitem class="osname">Solaris</systemitem>.
</para>
</sect1>
<sect1 id="auth-ldap">
<title>LDAP Authentication</title>
<indexterm zone="auth-ldap">
<primary>LDAP</primary>
</indexterm>
<para>
This authentication method operates similarly to
<literal>password</literal> except that it uses LDAP
as the password verification method. LDAP is used only to validate
the user name/password pairs. Therefore the user must already
exist in the database before LDAP can be used for
authentication.
</para>
<para>
LDAP authentication can operate in two modes. In the first mode,
which we will call the simple bind mode,
the server will bind to the distinguished name constructed as
<replaceable>prefix</replaceable> <replaceable>username</replaceable> <replaceable>suffix</replaceable>.
Typically, the <replaceable>prefix</replaceable> parameter is used to specify
<literal>cn=</literal>, or <replaceable>DOMAIN</replaceable><literal>\</literal> in an Active
Directory environment. <replaceable>suffix</replaceable> is used to specify the
remaining part of the DN in a non-Active Directory environment.
</para>
<para>
In the second mode, which we will call the search+bind mode,
the server first binds to the LDAP directory with
a fixed user name and password, specified with <replaceable>ldapbinddn</replaceable>
and <replaceable>ldapbindpasswd</replaceable>, and performs a search for the user trying
to log in to the database. If no user and password is configured, an
anonymous bind will be attempted to the directory. The search will be
performed over the subtree at <replaceable>ldapbasedn</replaceable>, and will try to
do an exact match of the attribute specified in
<replaceable>ldapsearchattribute</replaceable>.
Once the user has been found in
this search, the server disconnects and re-binds to the directory as
this user, using the password specified by the client, to verify that the
login is correct. This mode is the same as that used by LDAP authentication
schemes in other software, such as Apache <literal>mod_authnz_ldap</literal> and <literal>pam_ldap</literal>.
This method allows for significantly more flexibility
in where the user objects are located in the directory, but will cause
two separate connections to the LDAP server to be made.
</para>
<para>
The following configuration options are used in both modes:
<variablelist>
<varlistentry>
<term><literal>ldapserver</literal></term>
<listitem>
<para>
Names or IP addresses of LDAP servers to connect to. Multiple
servers may be specified, separated by spaces.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapport</literal></term>
<listitem>
<para>
Port number on LDAP server to connect to. If no port is specified,
the LDAP library's default port setting will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapscheme</literal></term>
<listitem>
<para>
Set to <literal>ldaps</literal> to use LDAPS. This is a non-standard
way of using LDAP over SSL, supported by some LDAP server
implementations. See also the <literal>ldaptls</literal> option for
an alternative.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldaptls</literal></term>
<listitem>
<para>
Set to 1 to make the connection between PostgreSQL and the LDAP server
use TLS encryption. This uses the <literal>StartTLS</literal>
operation per <ulink url="https://tools.ietf.org/html/rfc4513">RFC 4513</ulink>.
See also the <literal>ldapscheme</literal> option for an alternative.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
Note that using <literal>ldapscheme</literal> or
<literal>ldaptls</literal> only encrypts the traffic between the
PostgreSQL server and the LDAP server. The connection between the
PostgreSQL server and the PostgreSQL client will still be unencrypted
unless SSL is used there as well.
</para>
<para>
The following options are used in simple bind mode only:
<variablelist>
<varlistentry>
<term><literal>ldapprefix</literal></term>
<listitem>
<para>
String to prepend to the user name when forming the DN to bind as,
when doing simple bind authentication.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapsuffix</literal></term>
<listitem>
<para>
String to append to the user name when forming the DN to bind as,
when doing simple bind authentication.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The following options are used in search+bind mode only:
<variablelist>
<varlistentry>
<term><literal>ldapbasedn</literal></term>
<listitem>
<para>
Root DN to begin the search for the user in, when doing search+bind
authentication.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapbinddn</literal></term>
<listitem>
<para>
DN of user to bind to the directory with to perform the search when
doing search+bind authentication.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapbindpasswd</literal></term>
<listitem>
<para>
Password for user to bind to the directory with to perform the search
when doing search+bind authentication.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapsearchattribute</literal></term>
<listitem>
<para>
Attribute to match against the user name in the search when doing
search+bind authentication. If no attribute is specified, the
<literal>uid</literal> attribute will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapsearchfilter</literal></term>
<listitem>
<para>
The search filter to use when doing search+bind authentication.
Occurrences of <literal>$username</literal> will be replaced with the
user name. This allows for more flexible search filters than
<literal>ldapsearchattribute</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ldapurl</literal></term>
<listitem>
<para>
An <ulink url="https://tools.ietf.org/html/rfc4516">RFC 4516</ulink>
LDAP URL. This is an alternative way to write some of the
other LDAP options in a more compact and standard form. The format is
<synopsis>
ldap[s]://<replaceable>host</replaceable>[:<replaceable>port</replaceable>]/<replaceable>basedn</replaceable>[?[<replaceable>attribute</replaceable>][?[<replaceable>scope</replaceable>][?[<replaceable>filter</replaceable>]]]]
</synopsis>
<replaceable>scope</replaceable> must be one
of <literal>base</literal>, <literal>one</literal>, <literal>sub</literal>,
typically the last. (The default is <literal>base</literal>, which
is normally not useful in this application.) <replaceable>attribute</replaceable> can
nominate a single attribute, in which case it is used as a value for
<literal>ldapsearchattribute</literal>. If
<replaceable>attribute</replaceable> is empty then
<replaceable>filter</replaceable> can be used as a value for
<literal>ldapsearchfilter</literal>.
</para>
<para>
The URL scheme <literal>ldaps</literal> chooses the LDAPS method for
making LDAP connections over SSL, equivalent to using
<literal>ldapscheme=ldaps</literal>. To use encrypted LDAP
connections using the <literal>StartTLS</literal> operation, use the
normal URL scheme <literal>ldap</literal> and specify the
<literal>ldaptls</literal> option in addition to
<literal>ldapurl</literal>.
</para>
<para>
For non-anonymous binds, <literal>ldapbinddn</literal>
and <literal>ldapbindpasswd</literal> must be specified as separate
options.
</para>
<para>
LDAP URLs are currently only supported with
<productname>OpenLDAP</productname>, not on Windows.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
It is an error to mix configuration options for simple bind with options
for search+bind.
</para>
<para>
When using search+bind mode, the search can be performed using a single
attribute specified with <literal>ldapsearchattribute</literal>, or using
a custom search filter specified with
<literal>ldapsearchfilter</literal>.
Specifying <literal>ldapsearchattribute=foo</literal> is equivalent to
specifying <literal>ldapsearchfilter="(foo=$username)"</literal>. If neither
option is specified the default is
<literal>ldapsearchattribute=uid</literal>.
</para>
<para>
If <productname>PostgreSQL</productname> was compiled with
<productname>OpenLDAP</productname> as the LDAP client library, the
<literal>ldapserver</literal> setting may be omitted. In that case, a
list of host names and ports is looked up via
<ulink url="https://tools.ietf.org/html/rfc2782">RFC 2782</ulink> DNS SRV records.
The name <literal>_ldap._tcp.DOMAIN</literal> is looked up, where
<literal>DOMAIN</literal> is extracted from <literal>ldapbasedn</literal>.
</para>
<para>
Here is an example for a simple-bind LDAP configuration:
<programlisting>
host ... ldap ldapserver=ldap.example.net ldapprefix="cn=" ldapsuffix=", dc=example, dc=net"
</programlisting>
When a connection to the database server as database
user <literal>someuser</literal> is requested, PostgreSQL will attempt to
bind to the LDAP server using the DN <literal>cn=someuser, dc=example,
dc=net</literal> and the password provided by the client. If that connection
succeeds, the database access is granted.
</para>
<para>
Here is an example for a search+bind configuration:
<programlisting>
host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchattribute=uid
</programlisting>
When a connection to the database server as database
user <literal>someuser</literal> is requested, PostgreSQL will attempt to
bind anonymously (since <literal>ldapbinddn</literal> was not specified) to
the LDAP server, perform a search for <literal>(uid=someuser)</literal>
under the specified base DN. If an entry is found, it will then attempt to
bind using that found information and the password supplied by the client.
If that second connection succeeds, the database access is granted.
</para>
<para>
Here is the same search+bind configuration written as a URL:
<programlisting>
host ... ldap ldapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub"
</programlisting>
Some other software that supports authentication against LDAP uses the
same URL format, so it will be easier to share the configuration.
</para>
<para>
Here is an example for a search+bind configuration that uses
<literal>ldapsearchfilter</literal> instead of
<literal>ldapsearchattribute</literal> to allow authentication by
user ID or email address:
<programlisting>
host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchfilter="(|(uid=$username)(mail=$username))"
</programlisting>
</para>
<para>
Here is an example for a search+bind configuration that uses DNS SRV
discovery to find the host name(s) and port(s) for the LDAP service for the
domain name <literal>example.net</literal>:
<programlisting>
host ... ldap ldapbasedn="dc=example,dc=net"
</programlisting>
</para>
<tip>
<para>
Since LDAP often uses commas and spaces to separate the different
parts of a DN, it is often necessary to use double-quoted parameter
values when configuring LDAP options, as shown in the examples.
</para>
</tip>
</sect1>
<sect1 id="auth-radius">
<title>RADIUS Authentication</title>
<indexterm zone="auth-radius">
<primary>RADIUS</primary>
</indexterm>
<para>
This authentication method operates similarly to
<literal>password</literal> except that it uses RADIUS
as the password verification method. RADIUS is used only to validate
the user name/password pairs. Therefore the user must already
exist in the database before RADIUS can be used for
authentication.
</para>
<para>
When using RADIUS authentication, an Access Request message will be sent
to the configured RADIUS server. This request will be of type
<literal>Authenticate Only</literal>, and include parameters for
<literal>user name</literal>, <literal>password</literal> (encrypted) and
<literal>NAS Identifier</literal>. The request will be encrypted using
a secret shared with the server. The RADIUS server will respond to
this request with either <literal>Access Accept</literal> or
<literal>Access Reject</literal>. There is no support for RADIUS accounting.
</para>
<para>
Multiple RADIUS servers can be specified, in which case they will
be tried sequentially. If a negative response is received from
a server, the authentication will fail. If no response is received,
the next server in the list will be tried. To specify multiple
servers, separate the server names with commas and surround the list
with double quotes. If multiple servers are specified, the other
RADIUS options can also be given as comma-separated lists, to provide
individual values for each server. They can also be specified as
a single value, in which case that value will apply to all servers.
</para>
<para>
The following configuration options are supported for RADIUS:
<variablelist>
<varlistentry>
<term><literal>radiusservers</literal></term>
<listitem>
<para>
The DNS names or IP addresses of the RADIUS servers to connect to.
This parameter is required.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>radiussecrets</literal></term>
<listitem>
<para>
The shared secrets used when talking securely to the RADIUS
servers. This must have exactly the same value on the PostgreSQL
and RADIUS servers. It is recommended that this be a string of
at least 16 characters. This parameter is required.
<note>
<para>
The encryption vector used will only be cryptographically
strong if <productname>PostgreSQL</productname> is built with support for
<productname>OpenSSL</productname>. In other cases, the transmission to the
RADIUS server should only be considered obfuscated, not secured, and
external security measures should be applied if necessary.
</para>
</note>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>radiusports</literal></term>
<listitem>
<para>
The port numbers to connect to on the RADIUS servers. If no port
is specified, the default RADIUS port (<literal>1812</literal>)
will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>radiusidentifiers</literal></term>
<listitem>
<para>
The strings to be used as <literal>NAS Identifier</literal> in the
RADIUS requests. This parameter can be used, for example, to
identify which database cluster the user is attempting to connect
to, which can be useful for policy matching on
the RADIUS server. If no identifier is specified, the default
<literal>postgresql</literal> will be used.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
If it is necessary to have a comma or whitespace in a RADIUS parameter
value, that can be done by putting double quotes around the value, but
it is tedious because two layers of double-quoting are now required.
An example of putting whitespace into RADIUS secret strings is:
<programlisting>
host ... radius radiusservers="server1,server2" radiussecrets="""secret one"",""secret two"""
</programlisting>
</para>
</sect1>
<sect1 id="auth-cert">
<title>Certificate Authentication</title>
<indexterm zone="auth-cert">
<primary>Certificate</primary>
</indexterm>
<para>
This authentication method uses SSL client certificates to perform
authentication. It is therefore only available for SSL connections.
When using this authentication method, the server will require that
the client provide a valid, trusted certificate. No password prompt
will be sent to the client. The <literal>cn</literal> (Common Name)
attribute of the certificate
will be compared to the requested database user name, and if they match
the login will be allowed. User name mapping can be used to allow
<literal>cn</literal> to be different from the database user name.
</para>
<para>
The following configuration options are supported for SSL certificate
authentication:
<variablelist>
<varlistentry>
<term><literal>map</literal></term>
<listitem>
<para>
Allows for mapping between system and database user names. See
<xref linkend="auth-username-maps"/> for details.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
It is redundant to use the <literal>clientcert</literal> option with
<literal>cert</literal> authentication because <literal>cert</literal>
authentication is effectively <literal>trust</literal> authentication
with <literal>clientcert=verify-full</literal>.
</para>
</sect1>
<sect1 id="auth-pam">
<title>PAM Authentication</title>
<indexterm zone="auth-pam">
<primary>PAM</primary>
</indexterm>
<para>
This authentication method operates similarly to
<literal>password</literal> except that it uses PAM (Pluggable
Authentication Modules) as the authentication mechanism. The
default PAM service name is <literal>postgresql</literal>.
PAM is used only to validate user name/password pairs and optionally the
connected remote host name or IP address. Therefore the user must already
exist in the database before PAM can be used for authentication. For more
information about PAM, please read the
<ulink url="https://www.kernel.org/pub/linux/libs/pam/">
<productname>Linux-PAM</productname> Page</ulink>.
</para>
<para>
The following configuration options are supported for PAM:
<variablelist>
<varlistentry>
<term><literal>pamservice</literal></term>
<listitem>
<para>
PAM service name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>pam_use_hostname</literal></term>
<listitem>
<para>
Determines whether the remote IP address or the host name is provided
to PAM modules through the <symbol>PAM_RHOST</symbol> item. By
default, the IP address is used. Set this option to 1 to use the
resolved host name instead. Host name resolution can lead to login
delays. (Most PAM configurations don't use this information, so it is
only necessary to consider this setting if a PAM configuration was
specifically created to make use of it.)
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<note>
<para>
If PAM is set up to read <filename>/etc/shadow</filename>, authentication
will fail because the PostgreSQL server is started by a non-root
user. However, this is not an issue when PAM is configured to use
LDAP or other authentication methods.
</para>
</note>
</sect1>
<sect1 id="auth-bsd">
<title>BSD Authentication</title>
<indexterm zone="auth-bsd">
<primary>BSD Authentication</primary>
</indexterm>
<para>
This authentication method operates similarly to
<literal>password</literal> except that it uses BSD Authentication
to verify the password. BSD Authentication is used only
to validate user name/password pairs. Therefore the user's role must
already exist in the database before BSD Authentication can be used
for authentication. The BSD Authentication framework is currently
only available on OpenBSD.
</para>
<para>
BSD Authentication in <productname>PostgreSQL</productname> uses
the <literal>auth-postgresql</literal> login type and authenticates with
the <literal>postgresql</literal> login class if that's defined
in <filename>login.conf</filename>. By default that login class does not
exist, and <productname>PostgreSQL</productname> will use the default login class.
</para>
<note>
<para>
To use BSD Authentication, the PostgreSQL user account (that is, the
operating system user running the server) must first be added to
the <literal>auth</literal> group. The <literal>auth</literal> group
exists by default on OpenBSD systems.
</para>
</note>
</sect1>
<sect1 id="client-authentication-problems">
<title>Authentication Problems</title>
<para>
Authentication failures and related problems generally
manifest themselves through error messages like the following:
</para>
<para>
<programlisting>
FATAL: no pg_hba.conf entry for host "123.123.123.123", user "andym", database "testdb"
</programlisting>
This is what you are most likely to get if you succeed in contacting
the server, but it does not want to talk to you. As the message
suggests, the server refused the connection request because it found
no matching entry in its <filename>pg_hba.conf</filename>
configuration file.
</para>
<para>
<programlisting>
FATAL: password authentication failed for user "andym"
</programlisting>
Messages like this indicate that you contacted the server, and it is
willing to talk to you, but not until you pass the authorization
method specified in the <filename>pg_hba.conf</filename> file. Check
the password you are providing, or check your Kerberos or ident
software if the complaint mentions one of those authentication
types.
</para>
<para>
<programlisting>
FATAL: user "andym" does not exist
</programlisting>
The indicated database user name was not found.
</para>
<para>
<programlisting>
FATAL: database "testdb" does not exist
</programlisting>
The database you are trying to connect to does not exist. Note that
if you do not specify a database name, it defaults to the database
user name, which might or might not be the right thing.
</para>
<tip>
<para>
The server log might contain more information about an
authentication failure than is reported to the client. If you are
confused about the reason for a failure, check the server log.
</para>
</tip>
</sect1>
</chapter>