Merge 1.3.0 changes back to master.
diff --git a/src/chapters/docker.xml b/src/chapters/docker.xml
index c294226..0a19f5c 100644
--- a/src/chapters/docker.xml
+++ b/src/chapters/docker.xml
@@ -867,6 +867,47 @@
configured to use each when the Docker image starts.</para>
</section>
</section>
+ <section xml:id="guacamole-docker-header-auth">
+ <title>Header Authentication</title>
+ <para>The header authentication extension can be used to authenticate Guacamole
+ through a trusted third-party server, where the authenticated user's username
+ is passed back to Guacamole via a specific HTTP header. The following
+ are valid Docker variables for enabling and configuring header
+ authentication:</para>
+ <informaltable frame="all">
+ <tgroup cols="2">
+ <colspec colname="c1" colnum="1" colwidth="1*"/>
+ <colspec colname="c2" colnum="2" colwidth="2.25*"/>
+ <thead>
+ <row>
+ <entry>Variable</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><envar>HEADER_ENABLED</envar></entry>
+ <entry>
+ <para>Enables authentication via the header extension,
+ which causes the extension to be loaded when
+ Guacamole starts. By default this is false and the
+ header extension will not be loaded.</para>
+ </entry>
+ </row>
+ <row>
+ <entry><envar>HTTP_AUTH_HEADER</envar></entry>
+ <entry>
+ <para>Optional environment variable that, if set,
+ configures the name of the HTTP header that will
+ be used used to authenticate the user to
+ Guacamole. If this is not specified the default
+ value of REMOTE_USER will be used.</para>
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+ </section>
<section xml:id="guacamole-docker-guacamole-home">
<title>Custom extensions and <envar>GUACAMOLE_HOME</envar></title>
<para>If you have your own or third-party extensions for Guacamole which are not
