A bit more details about Kerberos and LDAP mappers in docs

docbook/auth-server-docs/reference/en/en-US/modules/kerberos.xml

@@ -154,7 +154,7 @@ ktadd -k /tmp/http.keytab HTTP/www.mydomain.org@MYDOMAIN.ORG
             </listitem>
             <listitem>
                 <para>
-                    Finally run Keycloak server and configure SPNEGO/Kerberos authentication in Keycloak admin console. Keycloak supports Kerberos authentication
+                    Run Keycloak server and configure SPNEGO/Kerberos authentication in Keycloak admin console. Keycloak supports Kerberos authentication
                     through <link linkend='user_federation'>Federation provider SPI</link> . We have 2 federation providers with Kerberos authentication support:
                     <variablelist>
                         <varlistentry>
@@ -185,6 +185,20 @@ ktadd -k /tmp/http.keytab HTTP/www.mydomain.org@MYDOMAIN.ORG
                     </variablelist>
                 </para>
             </listitem>
+            <listitem>
+                <para>
+                    Finally you may need to check the Kerberos authenticator correctly configured. You can go to <literal>Authentication</literal> tab in
+                    admin console and select <literal>Browser</literal> flow. Here you will see <literal>Kerberos</literal> authenticator, which is used by Keycloak for SPNEGO
+                    handshake with client (exchange <literal>Negotiate</literal> header etc.). By default it's disabled, so Keycloak doesn't ask for Negotiate header, however once you
+                    configured federation provider in previous step, it's automatically switched to <literal>ALTERNATIVE</literal>. So defacto you don't need to do anything, just
+                    check that it's really switched to Alternative.
+                </para>
+                <para>
+                    Alternative means that Keycloak tries to ask browser for Negotiate header, but if it's not available, it will continue on next authenticator (which usually means
+                    displaying username/password form to user). You can switch to <literal>REQUIRED</literal> if you want to enforce login with
+                    kerberos ticket and not allow fallback to username/password form.
+                </para>
+            </listitem>
         </itemizedlist>
     </section>
     <section>

docbook/auth-server-docs/reference/en/en-US/modules/user-federation.xml

@@ -294,8 +294,24 @@
             We have an example, which is showing LDAP integration and set of base mappers and sample mappers (mappers for street and postalCode) . It's in <literal>examples/ldap</literal>
             in the Keycloak example distribution or demo distribution download. You can also check the example sources directly <ulink url="https://github.com/keycloak/keycloak/blob/master/examples/ldap">here</ulink> .
         </para>
+        <section>
+            <title>Writing your own LDAP Mapper</title>
+            <para>
+                For the more advanced usecases, you have the possibility to create your own implementation of LDAP mapper or just subclass from
+                some already existing mapper implementation. You will need to implement <literal>UserFederationMapperFactory</literal> interface. In most cases, instead of
+                creating <literal>UserFederationMapperFactory</literal> from scratch, you can create subclasses of <literal>AbstractLDAPFederationMapperFactory</literal>, which itself
+                implements <literal>UserFederationMapperFactory</literal>. Then you need to create mapper implementation, which will be subclass of
+                <literal>AbstractLDAPFederationMapper</literal> (this mapper implementation will be returned by <literal>YourAbstractLDAPFederationMapperFactorySubclass.createMapper</literal> method).
+            </para>
+            <para>
+                After your code is written you must package up all your classes within a JAR file. This jar file must contain a file called
+                <literal>org.keycloak.mappers.UserFederationMapperFactory</literal> within the <literal>META-INF/services directory</literal> of the JAR. This file is a list of fully
+                qualified classnames of all implementations of <literal>UserFederationMapperFactory</literal>. For more details, look at section for
+                <link linkend="write_federation_provider">Write your own federation provider</link> and at <link linkend="providers">Providers and SPI</link> section.
+            </para>
+        </section>
     </section>
-    <section>
+    <section id="write_federation_provider">
         <title>Writing your own User Federation Provider</title>
         <para>
             The keycloak examples directory contains an example of a simple User Federation Provider backed by