src/chapters/custom-auth.xml

<?xml version="1.0" encoding="UTF-8"?>

<chapter xml:id="custom-authentication" xmlns="http://docbook.org/ns/docbook" version="5.0"
    xml:lang="en" xmlns:xi="http://www.w3.org/2001/XInclude">
    <title>Custom authentication</title>
    <indexterm xmlns:xl="http://www.w3.org/1999/xlink">
        <primary>authentication</primary>
        <secondary>custom</secondary>
    </indexterm>
    <para>Guacamole's authentication layer is designed to be extendable such that users can
        integrate Guacamole into existing authentication systems without having to resort to writing
        their own web application around the Guacamole API.</para>
    <para>The web application comes with a default authentication mechanism which uses an XML file
        to associate users with connections. Plugins for Guacamole that provide LDAP-based
        authentication or database-based authentication have also been developed.</para>
    <para>To demonstrate the principles involved, we will implement a very simple authentication
        plugin which associates a single user/password pair with a single connection, with all this
        information saved in properties inside the <filename>guacamole.properties</filename>
        file.</para>
    <para>In general, all other authentication plugins for Guacamole will use the principles
        demonstrated here. However, as of Guacamole 0.8.0, the authentication model has been
        significantly enhanced, and supports more than simply translating a username/password pair
        into a set of authorized configurations. This tutorial demonstrates the simplest way to
        create an authentication plugin for Guacamole - an authentication plugin that does not
        support management of users and connections via the web interface.</para>
    <section xml:id="auth-model">
        <title>Guacamole's authentication model</title>
        <para>When you view any page in Guacamole, whether that be the login screen or the client
            interface, the page makes an authentication attempt with the web application, sending
            all available credentials. After entering your username and password, the exact same
            process occurs, except the web application receives the username and password as
            well.</para>
        <para>The web application handles this authentication attempt by collecting all credentials
            available and passing them to a designated class called the "authentication provider".
            This class is designated via a property in the <filename>guacamole.properties</filename>
            file. Given the set of credentials, the specified authentication provider returns a
            context object that provides restricted access to other users and connections, if
            any.</para>
    </section>
    <section xml:id="client-plugin-skeleton">
        <title>A Guacamole plugin skeleton</title>
        <para>For simplicity's sake, and because this is how things are done upstream in the
            Guacamole project, we will use Maven to build our plugin.</para>
        <para>The bare minimum required for a Guacamole authentication plugin is a
                <filename>pom.xml</filename> file listing guacamole-ext as a dependency, and a
            single .java file implementing our stub of an authentication provider.</para>
        <para>In our stub, we won't actually do any authentication yet; we'll just universally
            reject all authentication attempts by returning <varname>null</varname> for any
            credentials given. You can verify that this is what happens by checking the server
            logs.</para>
        <example>
            <title>Barebones <filename>pom.xml</filename> required for a simple authentication
                plugin.</title>
            <programlisting>&lt;project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                        http://maven.apache.org/maven-v4_0_0.xsd">

    &lt;modelVersion>4.0.0&lt;/modelVersion>
    &lt;groupId>org.glyptodon.guacamole&lt;/groupId>
    &lt;artifactId>guacamole-auth-tutorial&lt;/artifactId>
    &lt;packaging>jar&lt;/packaging>
    &lt;version>0.8.0&lt;/version>
    &lt;name>guacamole-auth-tutorial&lt;/name>
    &lt;url>http://guac-dev.org/&lt;/url>

    &lt;properties>
        &lt;project.build.sourceEncoding>UTF-8&lt;/project.build.sourceEncoding>
    &lt;/properties>

    &lt;build>
        &lt;plugins>

            &lt;!-- Written for 1.6 -->
            &lt;plugin>
                &lt;groupId>org.apache.maven.plugins&lt;/groupId>
                &lt;artifactId>maven-compiler-plugin&lt;/artifactId>
                &lt;configuration>
                    &lt;source>1.6&lt;/source>
                    &lt;target>1.6&lt;/target>
                &lt;/configuration>
            &lt;/plugin>

        &lt;/plugins>
    &lt;/build>

    &lt;dependencies>

        &lt;!-- Guacamole Java API -->
        &lt;dependency>
            &lt;groupId>org.glyptodon.guacamole&lt;/groupId>
            &lt;artifactId>guacamole-common&lt;/artifactId>
            &lt;version>0.8.0&lt;/version>
        &lt;/dependency>

        &lt;!-- Guacamole Extension API -->
        &lt;dependency>
            &lt;groupId>org.glyptodon.guacamole&lt;/groupId>
            &lt;artifactId>guacamole-ext&lt;/artifactId>
            &lt;version>0.8.0&lt;/version>
        &lt;/dependency>

    &lt;/dependencies>

    &lt;repositories>
        
        &lt;!-- Central Guacamole repository -->
        &lt;repository>
            &lt;id>guac-dev&lt;/id>
            &lt;url>http://guac-dev.org/repo&lt;/url>
        &lt;/repository>
        
    &lt;/repositories>

&lt;/project></programlisting>
        </example>
        <para>We won't need to update this <filename>pom.xml</filename> throughout the rest of the
            tutorial. Even after adding new files, Maven will just find them and compile as
            necessary.</para>
        <para>Naturally, we need the actual authentication plugin skeleton code. While you can put
            this in whatever file and package you want, for the sake of this tutorial, we will
            assume you are using
                <classname>org.glyptodon.guacamole.auth.TutorialAuthenticationProvider</classname>.</para>
        <example>
            <title>A skeleton <classname>TutorialAuthenticationProvider</classname></title>
            <programlisting>package org.glyptodon.guacamole.auth;

import java.util.Map;
import org.glyptodon.guacamole.GuacamoleException;
import org.glyptodon.guacamole.net.auth.simple.SimpleAuthenticationProvider;
import org.glyptodon.guacamole.net.auth.Credentials;
import org.glyptodon.guacamole.protocol.GuacamoleConfiguration;

public class TutorialAuthenticationProvider extends SimpleAuthenticationProvider {
       
    @Override
    public Map&lt;String, GuacamoleConfiguration>
        getAuthorizedConfigurations(Credentials credentials)
        throws GuacamoleException {

        // Do nothing ... yet
        return null;        

    }

}</programlisting>
        </example>
        <para>To conform with Maven, this skeleton file must be placed within
                <filename>src/main/java/net/sourceforge/guacamole/auth</filename> as
                <filename>TutorialAuthenticationProvider.java</filename>.</para>
        <para>Notice how simple the authentication provider is. The
                <classname>AuthenticationProvider</classname> interface requires nothing more than a
            single <methodname>getAuthorizedConfigurations()</methodname> implementation, which must
            return a <classname>Map</classname> of <classname>GuacamoleConfiguration</classname>
            each associated with some arbitrary unique ID. This unique ID will be presented to the
            user in the connection list after they log in.</para>
        <para>For now, we just return <varname>null</varname>, which will cause Guacamole to report
            an invalid login for every attempt. Note that there is a difference in semantics between
            returning an empty map and returning <varname>null</varname>, as the former indicates
            the credentials are authorized but simply have no associated configurations, while the
            latter indicates the credentials are not authorized at all.</para>
    </section>
    <section xml:id="user-auth-example">
        <title>Actually authenticating the user</title>
        <para>Once we receive credentials, we need to validate those credentials against the
            associated properties in <filename>guacamole.properties</filename> (our source of
            authentication information for the sake of this tutorial).</para>
        <para>We will define four properties:<variablelist>
                <varlistentry>
                    <term><property>tutorial-user</property></term>
                    <listitem>
                        <para>The name of the only user we accept.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><property>tutorial-password</property></term>
                    <listitem>
                        <para>The password we require for the user specified to be
                            authenticated.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><property>tutorial-protocol</property></term>
                    <listitem>
                        <para>The protocol of the configuration this user is authorized to use,
                            which will be sent to guacd when the user logs in and selects their
                            connection.</para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term><property>tutorial-parameters</property></term>
                    <listitem>
                        <para>A comma-delimited list of
                                    <code><replaceable>name</replaceable>=<replaceable>value</replaceable></code>
                            pairs. For the sake of simplicity, we'll assume there will never be any
                            commas in the values.</para>
                    </listitem>
                </varlistentry>
            </variablelist></para>
        <para>If the username and password match what is stored in the file, we read the
            configuration information, store it in a <classname>GuacamoleConfiguration</classname>,
            and return the configuration within a set, telling Guacamole that this user is
            authorized but only to access the configurations returned.</para>
        <para>Upstream, we always place the properties of authentication providers in their own
            class, and so we will also do that here in this tutorial, as it keeps things
            organized.</para>
        <example>
            <title><filename>TutorialProperties.java</filename>, a class containing property
                definitions</title>
            <programlisting>package org.glyptodon.guacamole.auth;

import org.glyptodon.guacamole.properties.StringGuacamoleProperty;

public class TutorialGuacamoleProperties {

    /**
     * This class should not be instantiated.
     */
    private TutorialGuacamoleProperties() {}

    /**
     * The only user to allow.
     */
    public static final StringGuacamoleProperty TUTORIAL_USER = 
        new StringGuacamoleProperty() {

        @Override
        public String getName() { return "tutorial-user"; }

    };

    /**
     * The password required for the specified user.
     */
    public static final StringGuacamoleProperty TUTORIAL_PASSWORD = 
        new StringGuacamoleProperty() {

        @Override
        public String getName() { return "tutorial-password"; }

    };


    /**
     * The protocol to use when connecting.
     */
    public static final StringGuacamoleProperty TUTORIAL_PROTOCOL = 
        new StringGuacamoleProperty() {

        @Override
        public String getName() { return "tutorial-protocol"; }

    };


    /**
     * All parameters associated with the connection, as a comma-delimited
     * list of name="value" 
     */
    public static final StringGuacamoleProperty TUTORIAL_PARAMETERS = 
        new StringGuacamoleProperty() {

        @Override
        public String getName() { return "tutorial-parameters"; }

    };

}</programlisting>
        </example>
        <para>Normally, we would define a new type of <classname>GuacamoleProperty</classname> to
            handle the parsing of the parameters required by <varname>TUTORIAL_PARAMETERS</varname>,
            but for the sake of simplicity, parsing of this parameter will be embedded in the
            authentication function later.</para>
        <para>You will need to modify your existing <filename>guacamole.properties</filename> file,
            adding each of the above properties to describe one of your available
            connections.</para>
        <example>
            <title>Properties describing a user and connection, as required by this tutorial</title>
            <programlisting># Username and password
tutorial-user:     <replaceable>tutorial</replaceable>
tutorial-password: <replaceable>password</replaceable>

# Connection information
tutorial-protocol:   <replaceable>vnc</replaceable>
tutorial-parameters: <replaceable>hostname=localhost, port=5900</replaceable></programlisting>
        </example>
        <para>Once these properties and their accessor class are in place, it's simple enough to
            read the properties within <methodname>getAuthorizedConfigurations()</methodname> and
            authenticate the user based on their username and password.</para>
        <example>
            <title>Checking the credentials against the properties</title>
            <programlisting>@Override
public Map&lt;String, GuacamoleConfiguration>
    getAuthorizedConfigurations(Credentials credentials)
    throws GuacamoleException {

    // Get username
    String username = GuacamoleProperties.getRequiredProperty(
        TutorialProperties.TUTORIAL_USER
    );      

    // If wrong username, fail
    if (!username.equals(credentials.getUsername()))
        return null;

    // Get password
    String password = GuacamoleProperties.getRequiredProperty(
        TutorialProperties.TUTORIAL_PASSWORD
    );      

    // If wrong password, fail
    if (!password.equals(credentials.getPassword()))
        return null;

    // Successful login. Return configurations (STUB)
    return new HashMap&lt;String, GuacamoleConfiguration>();

}</programlisting>
        </example>
        <para>As is, the authentication provider will work in its current state in that the correct
            username and password will authenticate the user, while an incorrect username or
            password will not, but we still aren't returning an actual map of configurations. We
            need to construct the configuration based on the properties in the
                <filename>guacamole.properties</filename> file after the user has been
            authenticated, and return that configuration to the web application.</para>
    </section>
    <section xml:id="parse-conf-example">
        <title>Parsing the configuration</title>
        <para>The only remaining task before we have a fully-functioning authentication provider is
            to parse the configuration from the <filename>guacamole.properties</filename>
            file.</para>
        <example>
            <title>Parsing and returning a <classname>GuacamoleConfiguration</classname></title>
            <programlisting>@Override
public Map&lt;String, GuacamoleConfiguration>
    getAuthorizedConfigurations(Credentials credentials)
    throws GuacamoleException {

    // Get username
    String username = GuacamoleProperties.getRequiredProperty(
        TutorialProperties.TUTORIAL_USER
    );      

    // If wrong username, fail
    if (!username.equals(credentials.getUsername()))
        return null;

    // Get password
    String password = GuacamoleProperties.getRequiredProperty(
        TutorialProperties.TUTORIAL_PASSWORD
    );      

    // If wrong password, fail
    if (!password.equals(credentials.getPassword()))
        return null;

    // Successful login. Return configurations.
    Map&lt;String, GuacamoleConfiguration> configs = 
        new HashMap&lt;String, GuacamoleConfiguration>();

    // Create new configuration
    GuacamoleConfiguration config = new GuacamoleConfiguration();

    // Set protocol specified in properties
    config.setProtocol(GuacamoleProperties.getRequiredProperty(
        TutorialProperties.TUTORIAL_PROTOCOL
    ));

    // Set all parameters, splitting at commas
    for (String parameterValue : GuacamoleProperties.getRequiredProperty(
        TutorialProperties.TUTORIAL_PARAMETERS
    ).split(",\\s*")) {

        // Find the equals sign
        int equals = parameterValue.indexOf('=');
        if (equals == -1)
            throw new GuacamoleException("Required equals sign missing");

        // Get name and value from parameter string
        String name = parameterValue.substring(0, equals);
        String value = parameterValue.substring(equals+1);

        // Set parameter as specified
        config.setParameter(name, value);

    }

    configs.put("DEFAULT", config);
    return configs;

}</programlisting>
        </example>
    </section>
</chapter>