Add 'Using a Proxy Server with Authentication'

* Add note in SUSEConnect section
* Add section to Troubleshooting chapter in Admin Guide that
  refers to aforementioned note
* Add link to SUSEConnect section from Registration step in
  'Installing the Administration Node'

xml/admin_troubleshooting.xml

@@ -77,10 +77,24 @@
   </para>
  </sect1>
 
-<sect1 xml:id="sec.admin.troubleshooting.rbac">
+ <sect1 xml:id="sec.admin.troubleshooting.rbac">
   <title>RBAC/PSP</title>
   <para>
 
   </para>
  </sect1>
+
+ <sect1 xml:id="sec.admin.troubleshooting.proxy">
+  <title>Using a Proxy Server with Authentication</title>
+  <para>
+   If you need to register the &admin_node; with &scc; over a proxy
+   server that requires authentication, it is not possible to specify
+   the configuration in <filename>/etc/sysconfig/proxy</filename>.
+  </para>
+  <para>
+   For information about setting authentication credentials and
+   connecting to &scc; with <command>SUSEConnect</command>, see <xref
+   linkend="sec.configuration.suseconnect.proxy" />.
+  </para>
+ </sect1>
 </chapter>

xml/deployment_configuration.xml

@@ -787,6 +787,22 @@ runcmd:
    If you want to register your node at a &rmt; server, refer to the
    <emphasis>RMT Guide</emphasis> at <link xlink:href="https://www.suse.com/documentation/sles-15/book_rmt/data/book_rmt.html"/>.
   </para>
+  <note xml:id="sec.configuration.suseconnect.proxy">
+   <title>Using a Proxy Server with Authentication</title>
+   <para>
+    Create the file <filename>/root/.curlrc</filename> with the content:
+   </para>
+<screen>--proxy https://<replaceable>PROXY_FQDN</replaceable>:<replaceable>PROXY_PORT</replaceable>
+--proxy-user "<replaceable>USER</replaceable>:<replaceable>PASSWORD</replaceable>"</screen>
+   <para>
+    Replace <replaceable>PROXY_FQDN</replaceable> with the fully
+    qualified domain name of the proxy server and
+    <replaceable>PROXY_PORT</replaceable> with its port. Replace
+    <replaceable>USER</replaceable> and
+    <replaceable>PASSWORD</replaceable> with the credentials of an
+    allowed user for the proxy server.
+   </para>
+  </note>
  </sect1>
 
 </chapter>

xml/deployment_installing_nodes.xml

@@ -126,9 +126,12 @@
         <literal>https</literal> or <literal>http</literal>; other
         protocols are not supported. Fill this field to enable
         installing current updates during the installation process.
-        Alternatively, the machine can be registered at the &scc; or
-        a &smt; server at any later point in time with
-        <command>SUSEConnect</command>.
+        Alternatively, the machine can be registered at the &scc; or a
+        &smt; server at any later point in time with
+        <command>SUSEConnect</command>. For details about registering
+        with <command>SUSEConnect</command> and using an authenticated
+        proxy server for registration, see <xref
+        linkend="sec.configuration.suseconnect" />.
        </para>
       </listitem>
      </varlistentry>