<?xml version="1.0"?>
<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="realm-howto.html">

    &project;

    <properties>
        <author email="craigmcc@apache.org">Craig R. McClanahan</author>
        <title>Realm Configuration HOW-TO</title>
    </properties>

<body>


<section name="Table of Contents">

<p>
<a href="#Quick Start">Quick Start</a><br />
<blockquote>
<a href="#What is a Realm?">What is a Realm?</a><br />
<a href="#Configuring a Realm">Configuring a Realm</a><br />
</blockquote>
<a href="#Common Features">Common Features</a><br />
<blockquote>
<a href="#Digested Passwords">Digested Passwords</a><br />
<a href="#Example Application">Example Application</a><br />
<a href="#Manager Application">Manager Application</a><br />
<a href="#Realm Logging">Logging Within Realms</a><br />
</blockquote>
<a href="#Standard Realm Implementations">
Standard Realm Implementations</a><br />
<blockquote>
<a href="#JDBCRealm">JDBCRealm</a><br />
<a href="#DataSourceRealm">DataSourceRealm</a><br />
<a href="#JNDIRealm">JNDIRealm</a><br />
<a href="#MemoryRealm">MemoryRealm</a><br />
<a href="#JAASRealm">JAASRealm</a><br />
</blockquote>
</p>

</section>

<section name="Quick Start">

<p>This document describes how to configure Tomcat to support <em>container
managed security</em>, by connecting to an existing "database" of usernames,
passwords, and user roles.  You only need to care about this if you are using
a web application that includes one or more
<code>&lt;security-constraint&gt;</code> elements, and a
<code>&lt;login-config&gt;</code> element defining how users are required
to authenticate themselves.  If you are not utilizing these features, you can
safely skip this document.</p>

<p>For fundamental background information about container managed security,
see the <a href="http://java.sun.com/products/servlet/download.html">Servlet
Specification (Version 2.4)</a>, Section 12.</p>

<p>For information about utilizing the <em>Single Sign On</em> feature of
Tomcat 5 (allowing a user to authenticate themselves once across the entire
set of web applications associated with a virtual host), see
<a href="config/host.html#Single Sign On">here</a>.</p>

</section>


<section name="Overview">


<subsection name="What is a Realm?">

<p>A <strong>Realm</strong> is a "database" of usernames and passwords that
identify valid users of a web application (or set of web applications), plus
an enumeration of the list of <em>roles</em> associated with each valid user.
You can think of roles as similar to <em>groups</em> in Unix-like operating
systems, because access to specific web application resources is granted to
all users possessing a particular role (rather than enumerating the list of
associated usernames).  A particular user can have any number of roles
associated with their username.</p>

<p>Although the Servlet Specification describes a portable mechanism for
applications to <em>declare</em> their security requirements (in the
<code>web.xml</code> deployment descriptor), there is no portable API
defining the interface between a servlet container and the associated user
and role information.  In many cases, however, it is desireable to "connect"
a servlet container to some existing authentication database or mechanism
that already exists in the production environment.  Therefore, Tomcat 5
defines a Java interface (<code>org.apache.catalina.Realm</code>) that
can be implemented by "plug in" components to establish this connection.
Three standard plug-ins are provided, supporting connection to three different
sources of authentication information:</p>
<ul>
<li><a href="#DataSourceRealm">DataSourceRealm</a> - Accesses authentication
    information stored in a relational database, accessed via a named JNDI
    JDBC DataSource.</li>
<li><a href="#JDBCRealm">JDBCRealm</a> - Accesses authentication information
    stored in a relational database, accessed via a JDBC driver.</li>
<li><a href="#JNDIRealm">JNDIRealm</a> - Accesses authentication information
    stored in an LDAP based directory server, accessed via a JNDI provider.
    </li>
<li><a href="#MemoryRealm">MemoryRealm</a> - Accesses authentication
    information stored in an in-memory object collection, which is initialized
    from an XML document (<code>conf/tomcat-users.xml</code>).</li>
</ul>

<p>It is also possible to write your own <code>Realm</code> implementation,
and integrate it with Tomcat 5.  However, doing this is beyond the scope of
this document.  See (<strong>FIXME</strong> - reference to developer stuff)
for more information.</p>

</subsection>


<subsection name="Configuring a Realm">

<p>Before getting into the details of the standard Realm implementations, it is
important to understand, in general terms, how a Realm is configured.  In
general, you will be adding an XML element to your <code>conf/server.xml</code>
configuration file, that looks something like this:</p>

<source>
&lt;Realm className="... class name for this implementation"
       ... other attributes for this implementation .../&gt;
</source>

<p>The <code>&lt;Realm&gt;</code> element can be nested inside one of three
different elements, which has a direct impact on the "scope" of that Realm
(i.e. which web applications will share the same authentication information):
</p>
<ul>
<li><em>Inside an &lt;Engine&gt; element</em> - This Realm will be shared
    across ALL web applications on ALL virtual hosts, UNLESS it is overridden
    by a Realm element nested inside a subordinate <code>&lt;Host&gt;</code>
    or <code>&lt;Context&gt;</code> element.</li>
<li><em>Inside a &lt;Host&gt; element</em> - This Realm will be shared across
    ALL web applications for THIS virtual host, UNLESS it is overridden
    by a Realm element nested inside a subordinate <code>&lt;Context&gt;</code>
    element.</li>
<li><em>Inside a &lt;Context&gt; element</em> - This Realm will be used ONLY
    for THIS web application.</li>
</ul>


</subsection>


</section>


<section name="Common Features">


<subsection name="Digested Passwords">

<p>For each of the standard <code>Realm</code> implementations, the
user's password (by default) is stored in clear text.  In many
environments, this is undesireable because casual observers of the
authentication data can collect enough information to log on
successfully, and impersonate other users.  To avoid this problem, the
standard implementations support the concept of <em>digesting</em>
user passwords.  This allows the stored version of the passwords to be
encoded (in a form that is not easily reversible), but that the
<code>Realm</code> implementation can still utilize for
authentication.</p>

<p>When a standard realm authenticates by retrieving the stored
password and comparing it with the value presented by the user, you
can select digested passwords by specifying the <code>digest</code>
attribute on your <code>&lt;Realm&gt;</code> element.  The value for
this attribute must be one of the digest algorithms supported by the
<code>java.security.MessageDigest</code> class (SHA, MD2, or MD5).
When you select this option, the contents of the password that is
stored in the <code>Realm</code> must be the cleartext version of the
password, as digested by the specified algorithm.</p>

<p>When the <code>authenticate()</code> method of the Realm is called, the
(cleartext) password specified by the user is itself digested by the same
algorithm, and the result is compared with the value returned by the
<code>Realm</code>.  An equal match implies that the cleartext version of the
original password is the same as the one presented by the user, so that this
user should be authorized.</p>

<p>To calculate the digested value of a cleartext password, two convenience
techniques are supported:</p>
<ul>
<li>If you are writing an application that needs to calculate digested
    passwords dynamically, call the static <code>Digest()</code> method of the
    <code>org.apache.catalina.realm.RealmBase</code> class, passing the
    cleartext password and the digest algorithm name as arguments.  This
    method will return the digested password.</li>
<li>If you want to execute a command line utility to calculate the digested
    password, simply execute
<source>
java org.apache.catalina.realm.RealmBase \
    -a {algorithm} {cleartext-password}
</source>
    and the digested version of this cleartext password will be returned to
    standard output.</li>
</ul>

<p>To use either of the above techniques, the
<code>$CATALINA_HOME/server/lib/catalina.jar</code> file will need to be
on your class path to make the <code>RealmBase</code> class available.</p>

</subsection>


<subsection name="Example Application">

<p>The example application shipped with Tomcat 5 includes an area that is
protected by a security constraint, utilizing form-based login.  To access it,
point your browser at
<a href="http://localhost:8080/jsp-examples/security/protected/">http://localhost:8080/jsp-examples/security/protected/</a>
and log on with one of the usernames and passwords described for the default
<a href="#MemoryRealm">MemoryRealm</a>.</p>

</subsection>


<subsection name="Manager Application">

<p>If you wish to use the <a href="manager-howto.html">Manager Application</a>
to deploy and undeploy applications in a running Tomcat 5 installation, you
MUST add the "manager" role to at least one username in your selected Realm
implementation.  This is because the manager web application itself uses a
security constraint that requires role "manager" to access ANY request URI
within that application.</p>

<p>For security reasons, no username in the default Realm (i.e. using
<code>conf/tomcat-users.xml</code> is assigned the "manager" role.  Therfore,
no one will be able to utilize the features of this application until the
Tomcat administrator specifically assigns this role to one or more users.</p>

</subsection>

<subsection name="Realm Logging">

<p>Debugging and exception messages logged by a <code>Realm</code> will
   be recorded by the logging configuration associated with the container
   for the realm: its surrounding <a href="context.html">Context</a>,
   <a href="host.html">Host</a>, or <a href="engine.html">Engine</a>.</p>

</subsection>

</section>


<section name="Standard Realm Implementations">

<subsection name="JDBCRealm">

<h3>Introduction</h3>

<p><strong>JDBCRealm</strong> is an implementation of the Tomcat 5
<code>Realm</code> interface that looks up users in a relational database
accessed via a JDBC driver.  There is substantial configuration flexibility
that lets you adapt to existing table and column names, as long as your
database structure conforms to the following requirements:</p>
<ul>
<li>There must be a table, referenced below as the <em>users</em> table,
    that contains one row for every valid user that this <code>Realm</code>
    should recognize.</li>
<li>The <em>users</em> table must contain at least two columns (it may
    contain more if your existing applications required it):
    <ul>
    <li>Username to be recognized by Tomcat when the user logs in.</li>
    <li>Password to be recognized by Tomcat when the user logs in.
        This value may in cleartext or digested - see below for more
        information.</li>
    </ul></li>
<li>There must be a table, referenced below as the <em>user roles</em> table,
    that contains one row for every valid role that is assigned to a
    particular user.  It is legal for a user to have zero, one, or more than
    one valid role.</li>
<li>The <em>user roles</em> table must contain at least two columns (it may
    contain more if your existing applications required it):
    <ul>
    <li>Username to be recognized by Tomcat (same value as is specified
        in the <em>users</em> table).</li>
    <li>Role name of a valid role associated with this user.</li>
    </ul></li>
</ul>

<h3>Quick Start</h3>

<p>To set up Tomcat to use JDBCRealm, you will need to follow these steps:</p>
<ol>
<li>If you have not yet done so, create tables and columns in your database
    that conform to the requirements described above.</li>
<li>Configure a database username and password for use by Tomcat, that has
    at least read only access to the tables described above.  (Tomcat will
    never attempt to write to these tables.)</li>
<li>Place a copy of the JDBC driver you will be using inside the
    <code>$CATALINA_HOME/server/lib</code> directory (if you do not need it
    visible to web applications) or <code>$CATALINA_HOME/common/lib</code>
    (if it will be used both by Tomcat 5 <em>and</em> by your apps).
    Note that <strong>only</strong> JAR files are recognized!</li>
<li>Set up a <code>&lt;Realm&gt;</code> element, as described below, in your
    <code>$CATALINA_HOME/conf/server.xml</code> file.</li>
<li>Restart Tomcat 5 if it is already running.</li>
</ol>

<h3>Realm Element Attributes</h3>

<p>To configure JDBCRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_HOME/conf/server.xml</code> file,
as described <a href="#Configuring a Realm">above</a>.  The following
attributes are supported by this implementation:</p>

<attributes>

  <attribute name="className" required="true">
    <p>The fully qualified Java class name of this Realm implementation.
    You <strong>MUST</strong> specify the value
    "<code>org.apache.catalina.realm.JDBCRealm</code>" here.</p>
  </attribute>

  <attribute name="connectionName" required="true">
    <p>The database username used to establish a JDBC connection.</p>
  </attribute>

  <attribute name="connectionPassword" required="true">
    <p>The database password used to establish a JDBC connection.</p>
  </attribute>

  <attribute name="connectionURL" required="true">
    <p>The database URL used to establish a JDBC connection.</p>
  </attribute>

  <attribute name="digest" required="false">
    <p>The digest algorithm used to store passwords in non-plaintext formats.
    Valid values are those accepted for the algorithm name by the
    <code>java.security.MessageDigest</code> class.  See
    <a href="#Digested Passwords">Digested Passwords</a> for more
    information.  If not specified, passwords are stored in clear text.</p>
  </attribute>

  <attribute name="driverName" required="true">
    <p>The fully qualified Java class name of the JDBC driver to be used.
    Consult the documentation for your JDBC driver for the appropriate
    value.</p>
  </attribute>

  <attribute name="roleNameCol" required="true">
    <p>The name of the column, in the <em>user roles</em> table, that
    contains the name of a role assigned to this user.</p>
  </attribute>

  <attribute name="userCredCol" required="true">
    <p>The name of the column, in the <em>users</em> table, that contains
    the password for this user (either in clear text, or digested if the
    <code>digest</code> attribute is set).</p>
  </attribute>

  <attribute name="userNameCol" required="true">
    <p>The name of the column, in the <em>users</em> and <em>user roles</em>
    tables, that contains the username of this user.</p>
  </attribute>

  <attribute name="userRoleTable" required="true">
    <p>The name of the table that contains one row for each <em>role</em>
    assigned to a particular <em>username</em>.  This table must include at
    least the columns named by the <code>userNameCol</code> and
    <code>roleNameCol</code> attributes.</p>
  </attribute>

  <attribute name="userTable" required="true">
    <p>The name of the table that contains one row for each <em>username</em>
    to be recognized by Tomcat.  This table must include at least the columns
    named by the <code>userNameCol</code> and <code>userCredCol</code>
    attributes.</p>
  </attribute>

</attributes>

<h3>Example</h3>

<p>An example SQL script to create the needed tables might look something
like this (adapt the syntax as required for your particular database):</p>
<source>
create table users (
  user_name         varchar(15) not null primary key,
  user_pass         varchar(15) not null
);

create table user_roles (
  user_name         varchar(15) not null,
  role_name         varchar(15) not null,
  primary key (user_name, role_name)
);
</source>

<p>Example <code>Realm</code> elements are included (commented out) in the
default <code>$CATALINA_HOME/conf/server.xml</code> file.  Here's an example
for using a MySQL database called "authority", configured with the tables
described above, and accessed with username "dbuser" and password "dbpass":</p>
<source>
&lt;Realm className="org.apache.catalina.realm.JDBCRealm" debug="99"
      driverName="org.gjt.mm.mysql.Driver"
   connectionURL="jdbc:mysql://localhost/authority?user=dbuser&amp;amp;password=dbpass"
       userTable="users" userNameCol="user_name" userCredCol="user_pass"
   userRoleTable="user_roles" roleNameCol="role_name"/&gt;
</source>

<h3>Additional Notes</h3>

<p>JDBCRealm operates according to the following rules:</p>
<ul>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat 5 will call the <code>authenticate()</code> method of this
    <code>Realm</code>.  Thus, any changes you have made to the database
    directly (new users, changed passwords or roles, etc.) will be immediately
    reflected.</li>
<li>Once a user has been authenticated, the user (and his or her associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations. Any changes to the database
    information for an already authenticated user will <strong>not</strong> be
    reflected until the next time that user logs on again.</li>
<li>Administering the information in the <em>users</em> and <em>user roles</em>
    table is the responsibility of your own applications.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>

</subsection>


<subsection name="DataSourceRealm">

<h3>Introduction</h3>

<p><strong>DataSourceRealm</strong> is an implementation of the Tomcat 5
<code>Realm</code> interface that looks up users in a relational database
accessed via a JNDI named JDBC DataSource.  There is substantial configuration
flexibility that lets you adapt to existing table and column names, as long
as your database structure conforms to the following requirements:</p>
<ul>
<li>There must be a table, referenced below as the <em>users</em> table,
    that contains one row for every valid user that this <code>Realm</code>
    should recognize.</li>
<li>The <em>users</em> table must contain at least two columns (it may
    contain more if your existing applications required it):
    <ul>
    <li>Username to be recognized by Tomcat when the user logs in.</li>
    <li>Password to be recognized by Tomcat when the user logs in.
        This value may in cleartext or digested - see below for more
        information.</li>
    </ul></li>    
<li>There must be a table, referenced below as the <em>user roles</em> table,
    that contains one row for every valid role that is assigned to a
    particular user.  It is legal for a user to have zero, one, or more than
    one valid role.</li>
<li>The <em>user roles</em> table must contain at least two columns (it may
    contain more if your existing applications required it):
    <ul>
    <li>Username to be recognized by Tomcat (same value as is specified
        in the <em>users</em> table).</li>
    <li>Role name of a valid role associated with this user.</li>
    </ul></li>    
</ul>

<h3>Quick Start</h3>
                  
<p>To set up Tomcat to use DataSourceRealm, you will need to follow these steps:</p>
<ol>              
<li>If you have not yet done so, create tables and columns in your database
    that conform to the requirements described above.</li>
<li>Configure a database username and password for use by Tomcat, that has
    at least read only access to the tables described above.  (Tomcat will
    never attempt to write to these tables.)</li>
<li>Configure a JNDI named JDBC DataSource for your database.  Refer to the
    <a href="jndi-datasource-examples-howto.html">JNDI DataSource Example HOW-TO</a>
    for information on how to configure a JNDI named JDBC DataSource.</li>
<li>Set up a <code>&lt;Realm&gt;</code> element, as described below, in your
    <code>$CATALINA_HOME/conf/server.xml</code> file.</li>
<li>Restart Tomcat 5 if it is already running.</li>
</ol>

<h3>Realm Element Attributes</h3>

<p>To configure DataSourceRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_HOME/conf/server.xml</code> file,
as described <a href="#Configuring a Realm">above</a>.  The following
attributes are supported by this implementation:</p>

<attributes>

  <attribute name="className" required="true">
    <p>The fully qualified Java class name of this Realm implementation.
    You <strong>MUST</strong> specify the value
    "<code>org.apache.catalina.realm.DataSourceRealm</code>" here.</p>
  </attribute>

  <attribute name="dataSourceName" required="true">
    <p>The JNDI named JDBC DataSource for your database. If the DataSource is
    local to the context, the name is relative to <code>java:/comp/env</code>,
    and otherwise the name should match the name used to define the global
    DataSource.</p>
  </attribute>

  <attribute name="digest" required="false">
    <p>The digest algorithm used to store passwords in non-plaintext formats.
    Valid values are those accepted for the algorithm name by the
    <code>java.security.MessageDigest</code> class.  See
    <a href="#Digested Passwords">Digested Passwords</a> for more
    information.  If not specified, passwords are stored in clear text.</p>
  </attribute>
    
  <attribute name="localDataSource" required="false">
    <p>When the realm is nested inside a Context element, this allows the 
    realm to use a DataSource defined for the Context rather than a global
    DataSource.  If not specified, the default is <code>false</code>: use a 
    global DataSource.</p>
  </attribute>
    
  <attribute name="roleNameCol" required="true">
    <p>The name of the column, in the <em>user roles</em> table, that
    contains the name of a role assigned to this user.</p>
  </attribute>
    
  <attribute name="userCredCol" required="true">
    <p>The name of the column, in the <em>users</em> table, that contains
    the password for this user (either in clear text, or digested if the
    <code>digest</code> attribute is set).</p>
  </attribute>
    
  <attribute name="userNameCol" required="true">
    <p>The name of the column, in the <em>users</em> and <em>user roles</em>
    tables, that contains the username of this user.</p>
  </attribute>

  <attribute name="userRoleTable" required="true">
    <p>The name of the table that contains one row for each <em>role</em>
    assigned to a particular <em>username</em>.  This table must include at
    least the columns named by the <code>userNameCol</code> and
    <code>roleNameCol</code> attributes.</p>
  </attribute>

  <attribute name="userTable" required="true">
    <p>The name of the table that contains one row for each <em>username</em>
    to be recognized by Tomcat.  This table must include at least the columns
    named by the <code>userNameCol</code> and <code>userCredCol</code>
    attributes.</p>
  </attribute>

</attributes>

<h3>Example</h3>

<p>An example SQL script to create the needed tables might look something
like this (adapt the syntax as required for your particular database):</p>
<source>
create table users (
  user_name         varchar(15) not null primary key,
  user_pass         varchar(15) not null
);

create table user_roles (
  user_name         varchar(15) not null,
  role_name         varchar(15) not null,
  primary key (user_name, role_name)
);
</source>

<p>Here is an example for using a MySQL database called "authority", configured
with the tables described above, and accessed with the JNDI JDBC DataSource with
name "java:/comp/env/jdbc/authority".</p>
<source>
&lt;Realm className="org.apache.catalina.realm.DataSourceRealm" debug="99"
   dataSourceName="jdbc/authority"
   userTable="users" userNameCol="user_name" userCredCol="user_pass"
   userRoleTable="user_roles" roleNameCol="role_name"/&gt;
</source>

<h3>Additional Notes</h3>

<p>DataSourceRealm operates according to the following rules:</p>
<ul>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat 5 will call the <code>authenticate()</code> method of this
    <code>Realm</code>.  Thus, any changes you have made to the database
    directly (new users, changed passwords or roles, etc.) will be immediately
    reflected.</li>
<li>Once a user has been authenticated, the user (and his or her associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations. Any changes to the database
    information for an already authenticated user will <strong>not</strong> be
    reflected until the next time that user logs on again.</li>
<li>Administering the information in the <em>users</em> and <em>user roles</em>
    table is the responsibility of your own applications.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>

</subsection>


<subsection name="JNDIRealm">

<h3>Introduction</h3>

<p><strong>JNDIRealm</strong> is an implementation of the Tomcat 5
<code>Realm</code> interface that looks up users in an LDAP directory
server accessed by a JNDI provider (typically, the standard LDAP
provider that is available with the JNDI API classes). The realm
supports a variety of approaches to using a directory for
authentication.</p>

<h4>Connecting to the directory</h4>

<p>The realm's connection to the directory is defined by the
<strong>connectionURL</strong> configuration attribute. This is a URL
whose format is defined by the JNDI provider. It is usually an LDAP
URL that specifies the domain name of the directory server to connect
to, and optionally the port number and distinguished name (DN) of the
required root naming context.</p>

<p>If you have more than one provider you can configure an
<strong>alternateURL</strong>.  If a socket connection can not be
made to the provider at the <strong>connectionURL</strong> an
attempt will be made to use the <strong>alternateURL</strong>.</p>

<p>When making a connection in order to search the directory and
retrieve user and role information, the realm authenticates itself to
the directory with the username and password specified by the
<strong>connectionName</strong> and
<strong>connectionPassword</strong> properties. If these properties
are not specified the connection is anonymous. This is sufficient in
many cases.
</p>


<h4>Selecting the user's directory entry</h4>

<p>Each user that can be authenticated must be represented in the
directory by an individual entry that corresponds to an element in the
initial <code>DirContext</code> defined by the
<strong>connectionURL</strong> attribute. This user entry must have an
attribute containing the username that is presented for
authentication.</p>

<p>Often the distinguished name of the user's entry contains the
username presented for authentication but is otherwise the same for
all users. In this case the <strong>userPattern</strong> attribute may
be used to specify the DN, with "{0}" marking where
the username should be substituted.</p>

<p>Otherwise the realm must search the directory to find a unique entry
containing the username. The following attributes configure this
search:

     <ul>
     <li><strong>userBase</strong> - the entry that is the base of
         the subtree containing users.  If not specified, the search
         base is the top-level context.</li>

     <li><strong>userSubtree</strong> - the search scope. Set to
         <code>true</code> if you wish to search the entire subtree
         rooted at the <strong>userBase</strong> entry. The default value
         of <code>false</code> requests a single-level search
         including only the top level.</li>

     <li><strong>userSearch</strong> - pattern specifying the LDAP
         search filter to use after substitution of the username.</li>

    </ul>
</p>


<h4>Authenticating the user</h4>

<ul>
<li>
<p><b>Bind mode</b></p>

<p>By default the realm authenticates a user by binding to
the directory with the DN of the entry for that user and the password
presented by the user. If this simple bind succeeds the user is considered to
be authenticated.</p>

<p>For security reasons a directory may store a digest of the user's
password rather than the clear text version (see <a href="#Digested
Passwords">Digested Passwords</a> for more information). In that case,
as part of the simple bind operation the directory automatically
computes the correct digest of the plaintext password presented by the
user before validating it against the stored value. In bind mode,
therefore, the realm is not involved in digest processing. The
<strong>digest</strong> attribute is not used, and will be ignored if
set.</p>
</li>

<li>
<p><b>Comparison mode</b></p>
<p>Alternatively, the realm may retrieve the stored
password from the directory and compare it explicitly with the value
presented by the user. This mode is configured by setting the
<strong>userPassword</strong> attribute to the name of a directory
attribute in the user's entry that contains the password.</p>

<p>Comparison mode has some disadvantages. First, the
<strong>connectionName</strong> and
<strong>connectionPassword</strong> attributes must be configured to
allow the realm to read users' passwords in the directory. For
security reasons this is generally undesirable; indeed many directory
implementations will not allow even the directory manager to read
these passwords. In addition, the realm must handle password digests
itself, including variations in the algorithms used and ways of
representing password hashes in the directory. However, the realm may
sometimes need access to the stored password, for example to support
HTTP Digest Access Authentication (RFC 2069). (Note that HTTP digest
authentication is different from the storage of password digests in
the repository for user information as discussed above).
</p>
</li>
</ul>

<h4>Assigning roles to the user</h4>

<p>The directory realm supports two approaches to the representation
of roles in the directory:</p>

<ul>
<li>
<p><b>Roles as explicit directory entries</b></p>

<p>Roles may be represented by explicit directory entries. A role
entry is usually an LDAP group entry with one attribute
containing the name of the role and another whose values are the
distinguished names or usernames of the users in that role.  The
following attributes configure a directory search to
find the names of roles associated with the authenticated user:</p>

<ul>
<li><strong>roleBase</strong> - the base entry for the role search.
    If not specified, the search base is the top-level directory
    context.</li>

<li><strong>roleSubtree</strong> - the search
    scope. Set to <code>true</code> if you wish to search the entire
    subtree rooted at the <code>roleBase</code> entry. The default
    value of <code>false</code> requests a single-level search
    including the top level only.</li>

<li><strong>roleSearch</strong> - the LDAP search filter for
    selecting role entries. It optionally includes pattern
    replacements "{0}" for the distinguished name and/or "{1}" for the
    username of the authenticated user.</li>

<li><strong>roleName</strong> - the attribute in a role entry
     containing the name of that role.</li>

</ul>

</li>
</ul>

<ul>
<li>
<p><b>Roles as an attribute of the user entry</b></p>

<p>Role names may also be held as the values of an attribute in the
user's directory entry. Use <strong>userRoleName</strong> to specify
the name of this attribute.</p>

</li>
</ul>
<p>A combination of both approaches to role representation may be used.</p>

<h3>Quick Start</h3>

<p>To set up Tomcat to use JNDIRealm, you will need to follow these steps:</p>
<ol>
<li>Make sure your directory server is configured with a schema that matches
    the requirements listed above.</li>
<li>If required, configure a username and password for use by Tomcat, that has
    read only access to the information described above.  (Tomcat will
    never attempt to modify this information.)</li>
<li>Place a copy of the JNDI driver you will be using (typically
    <code>ldap.jar</code> available with JNDI) inside the
    <code>$CATALINA_HOME/server/lib</code> directory (if you do not need it
    visible to web applications) or <code>$CATALINA_HOME/common/lib</code>
    (if it will be used both by Tomcat 5 <em>and</em> by your apps).</li>
<li>Set up a <code>&lt;Realm&gt;</code> element, as described below, in your
    <code>$CATALINA_HOME/conf/server.xml</code> file.</li>
<li>Restart Tomcat 5 if it is already running.</li>
</ol>

<h3>Realm Element Attributes</h3>

<p>To configure JNDIRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_HOME/conf/server.xml</code> file,
as described <a href="#Configuring a Realm">above</a>.  The following
attributes are supported by this implementation:</p>

<attributes>
  <attribute name="className" required="true">
    <p>The fully qualified Java class name of this Realm implementation.
    You <strong>MUST</strong> specify the value
    "<code>org.apache.catalina.realm.JNDIRealm</code>" here.</p>
  </attribute>


      <attribute name="connectionName" required="false">
        <p>The directory username to use when establishing a
        connection to the directory for LDAP search operations. If not
        specified an anonymous connection is made, which is often
        sufficient unless you specify the <code>userPassword</code>
        property.</p>
      </attribute>

      <attribute name="connectionPassword" required="false">
        <p>The directory password to use when establishing a
        connection to the directory for LDAP search operations. If not
        specified an anonymous connection is made, which is often
        sufficient unless you specify the <code>userPassword</code>
        property.</p>
      </attribute>

      <attribute name="connectionURL" required="true">
        <p>The connection URL to be passed to the JNDI driver when
        establishing a connection to the directory.</p>
      </attribute>

      <attribute name="contextFactory" required="false">
        <p>The fully qualified Java class name of the JNDI context
        factory to be used for this connection.  By default, the standard
        JNDI LDAP provider is used
        (<code>com.sun.jndi.ldap.LdapCtxFactory</code>).</p>
      </attribute>

      <attribute name="digest" required="false">
        <p>The digest algorithm to apply to the plaintext password offered
        by the user before comparing it with the value retrieved from the
        directory.  Valid values are those accepted for the algorithm name
        by the <code>java.security.MessageDigest</code> class.  See <a
        href="#Digested Passwords">Digested Passwords</a> for more
        information. If not specified the plaintext password is assumed to
        be retrieved. Not required unless <code>userPassword</code> is
        specified</p>
      </attribute>

      <attribute name="roleBase" required="false">
        <p>The base directory entry for performing role searches. If
        not specified, the top level element in the directory context
        will be used.</p>
      </attribute>

      <attribute name="roleName" required="false">
        <p>The name of the attribute that contains role names in the
        directory entries found by a role search. In addition you can
        use the <code>userRoleName</code> property to specify the name
        of an attribute, in the user's entry, containing additional
        role names.  If <code>roleName</code> is not specified a role
        search does not take place, and roles are taken only from the
        user's entry.</p>
      </attribute>

      <attribute name="roleSearch" required="false">
        <p>The LDAP filter expression used for performing role
        searches, following the syntax supported by the
        <code>java.text.MessageFormat</code> class.  Use
        <code>{0}</code> to substitute the distinguished name (DN) of
        the user, and/or <code>{1}</code> to substitute the
        username. If not specified a role search does not take place
        and roles are taken only from the attribute in the user's
        entry specified by the <code>userRoleName</code> property.</p>
      </attribute>

      <attribute name="roleSubtree" required="false">
        <p>Set to <code>true</code> if you want to search the entire
        subtree of the element specified by the <code>roleBase</code>
        property for role entries associated with the user. The
        default value of <code>false</code> causes only the top level
        to be searched.</p>
      </attribute>

      <attribute name="userBase" required="false">
        <p>The base element for user searches performed using the
        <code>userSearch</code> expression.  If not specified, the top
        level element in the directory context will be used. Not used
        if you are using the <code>userPattern</code> expression.</p>
      </attribute>

      <attribute name="userPassword" required="false">
        <p>Name of the attribute in the user's entry containing the
        user's password.  If you specify this value, JNDIRealm will
        bind to the directory using the values specified by
        <code>connectionName</code> and
        <code>connectionPassword</code> properties, and retrieve the
        corresponding attribute for comparison to the value specified
        by the user being authenticated.  If the <code>digest</code>
        attribute is set, the specified digest algorithm is applied to
        the password offered by the user before comparing it with the
        value retrieved from the directory.  If you do
        <strong>not</strong> specify this value, JNDIRealm will
        attempt a simple bind to the directory using the DN of the
        user's entry and password specified by the user, with a
        successful bind being interpreted as an authenticated
        user.</p>
      </attribute>

      <attribute name="userPattern" required="false">
        <p>A pattern for the distinguished name (DN) of the user's
        directory entry, following the syntax supported by the
        <code>java.text.MessageFormat</code> class with
        <code>{0}</code> marking where the actual username should be
        inserted. You can use this property instead of
        <code>userSearch</code>, <code>userSubtree</code> and
        <code>userBase</code> when the distinguished name contains the
        username and is otherwise the same for all users.</p>
      </attribute>

      <attribute name="userRoleName" required="false">
        <p>The name of an attribute in the user's directory entry
        containing zero or more values for the names of roles assigned
        to this user.  In addition you can use the
        <code>roleName</code> property to specify the name of an
        attribute to be retrieved from individual role entries found
        by searching the directory. If <code>userRoleName</code> is
        not specified all the roles for a user derive from the role
        search.</p>
      </attribute>

      <attribute name="userSearch" required="false">
        <p>The LDAP filter expression to use when searching for a
        user's directory entry, with <code>{0}</code> marking where
        the actual username should be inserted.  Use this property
        (along with the <code>userBase</code> and
        <code>userSubtree</code> properties) instead of
        <code>userPattern</code> to search the directory for the
        user's entry.</p>
      </attribute>

      <attribute name="userSubtree" required="false">
        <p>Set to <code>true</code> if you want to search the entire
        subtree of the element specified by the <code>userBase</code>
        property for the user's entry. The default value of
        <code>false</code> causes only the top level to be searched.
        Not used if you are using the <code>userPattern</code>
        expression.</p>
      </attribute>

</attributes>

<h3>Example</h3>

<p>Creation of the appropriate schema in your directory server is beyond the
scope of this document, because it is unique to each directory server
implementation.  In the examples below, we will assume that you are using a
distribution of the OpenLDAP directory server (version 2.0.11 or later), which
can be downloaded from
<a href="http://www.openldap.org">http://www.openldap.org</a>.  Assume that
your <code>slapd.conf</code> file contains the following settings
(among others):</p>
<source>
database ldbm
suffix dc="mycompany",dc="com"
rootdn "cn=Manager,dc=mycompany,dc=com"
rootpw secret
</source>

<p>We will assume for <code>connectionURL</code> that the directory
server runs on the same machine as Tomcat.  See <a
href="http://java.sun.com/products/jndi/docs.html">http://java.sun.com/products/jndi/docs.html</a>
for more information about configuring and using the JNDI LDAP
provider.</p>

<p>Next, assume that this directory server has been populated with elements
as shown below (in LDIF format):</p>

<source>

# Define top-level entry
dn: dc=mycompany,dc=com
objectClass: dcObject
dc:mycompany

# Define an entry to contain people
# searches for users are based on this entry
dn: ou=people,dc=mycompany,dc=com
objectClass: organizationalUnit
ou: people

# Define a user entry for Janet Jones
dn: uid=jjones,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: jjones
sn: jones
cn: janet jones
mail: j.jones@mycompany.com
userPassword: janet

# Define a user entry for Fred Bloggs
dn: uid=fbloggs,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: fbloggs
sn: bloggs
cn: fred bloggs
mail: f.bloggs@mycompany.com
userPassword: fred

# Define an entry to contain LDAP groups
# searches for roles are based on this entry
dn: ou=groups,dc=mycompany,dc=com
objectClass: organizationalUnit
ou: groups

# Define an entry for the "tomcat" role
dn: cn=tomcat,ou=groups,dc=mycompany,dc=com
objectClass: groupOfUniqueNames
cn: tomcat
uniqueMember: uid=jjones,ou=people,dc=mycompany,dc=com
uniqueMember: uid=fbloggs,ou=people,dc=mycompany,dc=com

# Define an entry for the "role1" role
dn: cn=role1,ou=groups,dc=mycompany,dc=com
objectClass: groupOfUniqueNames
cn: role1
uniqueMember: uid=fbloggs,ou=people,dc=mycompany,dc=com
</source>

<p>An example <code>Realm</code> element for the OpenLDAP directory
server configured as described above might look like this, assuming
that users use their uid (e.g. jjones) to login to the
application and that an anonymous connection is sufficient to search
the directory and retrieve role information:</p>

<source>
&lt;Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
     connectionURL="ldap://localhost:389"
       userPattern="uid={0},ou=people,dc=mycompany,dc=com"
          roleBase="ou=groups,dc=mycompany,dc=com"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
/&gt;
</source>

<p>With this configuration, the realm will determine the user's
distinguished name by substituting the username into the
<code>userPattern</code>, authenticate by binding to the directory
with this DN and the password received from the user, and search the
directory to find the user's roles.</p>

<p>Now suppose that users are expected to enter their email address
rather than their userid when logging in. In this case the realm must
search the directory for the user's entry. (A search is also necessary
when user entries are held in multiple subtrees corresponding perhaps
to different organizational units or company locations).</p>

<p>Further, suppose that in addition to the group entries you want to
use an attribute of the user's entry to hold roles. Now the entry for
Janet Jones might read as follows:</p>

<source>
dn: uid=jjones,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: jjones
sn: jones
cn: janet jones
mail: j.jones@mycompany.com
memberOf: role2
memberOf: role3
userPassword: janet
</source>

<p> This realm configuration would satisfy the new requirements:</p>

<source>
&lt;Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
     connectionURL="ldap://localhost:389"
          userBase="ou=people,dc=mycompany,dc=com"
        userSearch="(mail={0})"
      userRoleName="memberOf"
          roleBase="ou=groups,dc=mycompany,dc=com"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
/&gt;
</source>

<p>Now when Janet Jones logs in as "j.jones@mycompany.com", the realm
searches the directory for a unique entry with that value as its mail
attribute and attempts to bind to the directory as
<code>uid=jjones,ou=people,dc=mycompany,dc=com</code> with the given
password. If authentication succeeds, she is assigned three roles:
"role2" and "role3", the values of the "memberOf" attribute in her
directory entry, and "tomcat", the value of the "cn" attribute in the
only group entry of which she is a member.</p>

<p>Finally, to authenticate the user by retrieving
the password from the directory and making a local comparison in the
realm, you might use a realm configuration like this:</p>

<source>
&lt;Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
    connectionName="cn=Manager,dc=mycompany,dc=com"
connectionPassword="secret"
     connectionURL="ldap://localhost:389"
      userPassword="userPassword"
       userPattern="uid={0},ou=people,dc=mycompany,dc=com"
          roleBase="ou=groups,dc=mycompany,dc=com"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
/&gt;
</source>

<p>However, as discussed above, the default bind mode for
authentication is usually to be preferred.</p>

<h3>Additional Notes</h3>

<p>JNDIRealm operates according to the following rules:</p>
<ul>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat 5 will call the <code>authenticate()</code> method of this
    <code>Realm</code>.  Thus, any changes you have made to the directory
    (new users, changed passwords or roles, etc.) will be immediately
    reflected.</li>
<li>Once a user has been authenticated, the user (and his or her associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations. Any changes to the directory
    information for an already authenticated user will <strong>not</strong> be
    reflected until the next time that user logs on again.</li>
<li>Administering the information in the directory server
    is the responsibility of your own applications.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>

</subsection>


<subsection name="MemoryRealm">

<h3>Introduction</h3>

<p><strong>MemoryRealm</strong> is a simple demonstration implementation of the
Tomcat 5 <code>Realm</code> interface.  It is not designed for production use.
At startup time, MemoryRealm loads information about all users, and their
corresponding roles, from an XML document (by default, this document is loaded from <code>$CATALINA_HOME/conf/tomcat-users.xml</code>).  Changes to the data
in this file are not recognized until Tomcat is restarted.</p>

<h3>Realm Element Attributes</h3>

<p>To configure MemoryRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_HOME/conf/server.xml</code> file,
as described <a href="#Configuring a Realm">above</a>.  The following
attributes are supported by this implementation:</p>

<attributes>

  <attribute name="className" required="true">
    <p>The fully qualified Java class name of this Realm implementation.
    You <strong>MUST</strong> specify the value
    "<code>org.apache.catalina.realm.MemoryRealm</code>" here.</p>
  </attribute>

  <attribute name="digest" required="false">
    <p>The digest algorithm used to store passwords in non-plaintext formats.
    Valid values are those accepted for the algorithm name by the
    <code>java.security.MessageDigest</code> class.  See
    <a href="#Digested Passwords">Digested Passwords</a> for more
    information.  If not specified, passwords are stored in clear text.</p>
  </attribute>

  <attribute name="pathname" required="false">
    <p>Absolute or relative (to $CATALINA_HOME) pathname of the XML document
    containing our valid usernames, passwords, and roles.  See below for more
    information on the format of this file.  If not specified, the value
    <code>conf/tomcat-users.xml</code> is used.</p>
  </attribute>

</attributes>

<h3>User File Format</h3>

<p>The users file (by default, <code>conf/tomcat-users.xml</code> must be an
XML document, with a root element <code>&lt;tomcat-users&gt;</code>.  Nested
inside the root element will be a <code>&lt;user&gt;</code> element for each
valid user, consisting of the following attributes:</p>
<ul>
<li><strong>name</strong> - Username this user must log on with.</li>
<li><strong>password</strong> - Password this user must log on with (in
    clear text if the <code>digest</code> attribute was not set on the
    <code>&lt;Realm&gt;</code> element, or digested appropriately as
    described <a href="#Digested Passwords">here</a> otherwise).</li>
<li><strong>roles</strong> - Comma-delimited list of the role names
    associated with this user.</li>
</ul>

<h3>Example</h3>

<p>The default installation of Tomcat 5 is configured with a MemoryRealm
nested inside the <code>&lt;Engine&gt;</code> element, so that it applies
to all virtual hosts and web applications.  The default contents of the
<code>conf/tomcat-users.xml</code> file is:</p>
<source>
&lt;tomcat-users&gt;
  &lt;user name="tomcat" password="tomcat" roles="tomcat" /&gt;
  &lt;user name="role1"  password="tomcat" roles="role1"  /&gt;
  &lt;user name="both"   password="tomcat" roles="tomcat,role1" /&gt;
&lt;/tomcat-users&gt;
</source>

<h3>Additional Notes</h3>

<p>MemoryRealm operates according to the following rules:</p>
<ul>
<li>When Tomcat first starts up, it loads all defined users and their
    associated information from the users file.  Changes to the data in
    this file will <strong>not</strong> be recognized until Tomcat is
    restarted.</li>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat 5 will call the <code>authenticate()</code> method of this
    <code>Realm</code>.</li>
<li>Once a user has been authenticated, the user (and his or her associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations.</li>
<li>Administering the information in the users file is the responsibility
    of your application.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>


</subsection>


<subsection name="JAASRealm">

<h3>Introduction</h3>

        <p><strong>JAASRealm</strong> is an implementation of the Tomcat
4 <code>Realm</code> interface that authenticates users through the Java
Authentication &amp; Authorization Service (JAAS) framework, a Java
package that is available as an optional package in Java 2 SDK 1.3 and
is fully integrated as of SDK 1.4 .</p>
        <p>Using JAASRealm gives the developer the ability to combine
practically any conceivable security realm with Tomcat's CMA. </p>
        <p>JAASRealm is prototype for Tomcat of the proposed JAAS-based
J2EE authentication framework for J2EE v1.4, based on the <a
 href="http://www.jcp.org/en/jsr/detail?id=196">JCP Specification
Request 196</a> to enhance container-managed security and promote
'pluggable' authentication mechanisms whose implementations would be
container-independent.
        </p>
        <p>Based on the JAAS login module and principal (see <code>javax.security.auth.spi.LoginModule</code>
and <code>javax.security.Principal</code>), you can develop your own
security mechanism or wrap another third-party mechanism for
integration with the CMA as implemented by Tomcat.
        </p>

        <h3>Quick Start</h3>
        <p>To set up Tomcat to use JAASRealm with your own JAAS login module,
 you will need to follow these steps:</p>
        <ol>
          <li>Write your own LoginModule, User and Role classes based
on JAAS (see 
<a href="http://java.sun.com/j2se/1.4.1/docs/guide/security/jaas/tutorials/GeneralAcnOnly.html">the
JAAS Authentication Tutorial</a> and 
<a href="http://java.sun.com/j2se/1.4.1/docs/guide/security/jaas/JAASLMDevGuide.html">the JAAS Login Module 
Developer's Guide</a>) to be managed by the JAAS Login
Context (<code>javax.security.auth.login.LoginContext</code>)
          </li>
          <li>Although not specified in JAAS, you should create
seperate classes to distinguish between users and roles, extending <code>javax.security.Principal</code>,
so that Tomcat can tell which Principals returned from your login
module are users and which are roles (see <code>org.apache.catalina.realm.JAASRealm</code>).
          </li>
          <li>Place the compiled classes on Tomcat's classpath
          </li>
          <li>Set up a login.config file for Java (see <a
 href="http://java.sun.com/j2se/1.4.1/docs/guide/security/jaas/tutorials/LoginConfigFile.html">JAAS
LoginConfig file</a>) and tell Tomcat where to find it by specifying
its location to the JVM, for instance by setting the environment
variable: JAVA_OPTS=-D<code>JAVA_OPTS=-Djava.security.auth.login.config==$CATALINA_HOME/conf/jaas.config</code></li>
          <li>Configure your security-constraints in your web.xml for
the resources you want to protect</li>
          <li>Configure the JAASRealm module in your server.xml </li>
          <li>Restart Tomcat 4 if it is already running.</li>
        </ol>
        <h3>Realm Element Attributes</h3>
        <p>To configure JAASRealm as for step 6 above, you create
a <code>&lt;Realm&gt;</code> element and nest it in your 
<code>$CATALINA_HOME/conf/server.xml</code>
file within your <code>&lt;Engine&gt;</code> node. The following attributes 
are supported by this implementation:</p>

<attributes>

  <attribute name="className" required="true">
    <p>The fully qualified Java class name of this Realm implementation.
    You <strong>MUST</strong> specify the value
    "<code>org.apache.catalina.realm.MemoryRealm</code>" here.</p>
  </attribute>

  <attribute name="appName" required="true">
    <p>The name of the realm as configured in your login configuration file 
    (<a href="http://java.sun.com/j2se/1.4.1/docs/guide/security/jaas/tutorials/LoginConfigFile.html">JAAS LoginConfig</a>).</p>
  </attribute>

  <attribute name="userClassNames" required="true">
    <p>A comma-seperated list of the names of the classes that you have made 
    for your user <code>Principals</code>.</p>
  </attribute>

  <attribute name="roleClassNames" required="false">
    <p>A comma-seperated list of the names of the classes that you have made 
    for your role <code>Principals</code>.</p>
  </attribute>

</attributes>

<h3>Example</h3>

<p>Here is an example of how your server.xml snippet should look.</p>

<source>
&lt;Realm className="org.apache.catalina.realm.JAASRealm"                 
                appName="MyFooRealm"       
    userClassNames="org.foobar.realm.FooUser"       
     roleClassNames="org.foobar.realm.FooRole" 
                      debug="99"/&gt;
</source>

<p>It is the responsibility of your login module to create and save User and 
Role objects representing Principals for the user 
(<code>javax.security.auth.Subject</code>). If your login module doesn't 
create a user object but also doesn't throw a login exception, then the 
Tomcat CMA will break and you will be left at the 
http://localhost:8080/myapp/j_security_check URI or at some other 
unspecified location.</p>

        <p>The flexibility of the JAAS approach is two-fold: </p>
        <ul>
          <li>you can carry out whatever processing you require behind
the scenes in your own login module.</li>
          <li>you can plug in a completely different LoginModule by changing the configuration 
and restarting the server, without any code changes to your application.</li>
        </ul>

        <h3>Additional Notes</h3>
        <ul>
          <li>When a user attempts to access a protected resource for
              the first time, Tomcat 4 will call the <code>authenticate()</code>
              method of this <code>Realm</code>.  Thus, any changes you have made in
              the security mechanism directly (new users, changed passwords or
              roles, etc.) will be immediately reflected.</li>
          <li>Once a user has been authenticated, the user (and his or
              her associated roles) are cached within Tomcat for the duration of
              the user's login.  For FORM-based authentication, that means until
              the session times out or is invalidated; for BASIC authentication,
              that means until the user closes their browser.  Any changes to the
              security information for an already authenticated user will <strong>not</strong>
              be reflected until the next time that user logs on again.</li>
        </ul>

</subsection>


</section>

</body>

</document>