Add Kerberos/SPNEGO Shield custom realm

Closes #14282

docs/plugins/security.asciidoc

@@ -18,7 +18,10 @@ mind when it comes to protecting your data.
 [float]
 === Community contributed security plugins
 
-The following plugin has been contributed by our community:
+The following plugins have been contributed by our community:
+
+* https://github.com/codecentric/elasticsearch-shield-kerberos-realm[Kerberos/SPNEGO Realm]:
+  Custom Shield realm to Authenticate HTTP and Transport requests via Kerberos/SPNEGO (by codecentric AG)
 
 * https://github.com/sscarduzio/elasticsearch-readonlyrest-plugin[Readonly REST]:
   High performance access control for Elasticsearch native REST API (by Simone Scarduzio)
@@ -26,4 +29,4 @@ The following plugin has been contributed by our community:
 This community plugin appears to have been abandoned:
 
 * https://github.com/sonian/elasticsearch-jetty[Jetty HTTP transport plugin]:
-  Uses Jetty to provide SSL connections, basic authentication, and request logging (by Sonian Inc.)
+  Uses Jetty to provide SSL connections, basic authentication, and request logging (by Sonian Inc.)