Docsp 17095 java subject (#147)

Author: biniona-mongodb

source/fundamentals/enterprise-auth.txt

@@ -158,11 +158,21 @@ You may need to specify one or more of the following additional
       - :java-docs:`JAVA_SASL_CLIENT_PROPERTIES_KEY <apidocs/mongodb-driver-core/com/mongodb/MongoCredential.html#JAVA_SASL_CLIENT_PROPERTIES_KEY>`
       - :java-docs:`JAVA_SUBJECT_PROVIDER_KEY <apidocs/mongodb-driver-core/com/mongodb/MongoCredential.html#JAVA_SUBJECT_PROVIDER_KEY>`
 
-      Your code to instantiate a ``MongoClient`` using GSSAPI and additional
-      properties might look something like this:
+      Select the **SERVICE_NAME_KEY** or **JAVA_SUBJECT_KEY** tab to
+      see sample code to instantiate a ``MongoCredential`` that uses GSSAPI and
+      the selected property:
+
+      .. tabs::
+
+         .. tab::
+            :tabid: SERVICE_NAME_KEY
 
-      .. include:: /includes/fundamentals/code-snippets/auth-credentials-gssapi-properties.rst
+            .. include:: /includes/fundamentals/code-snippets/auth-credentials-gssapi-properties.rst
 
+         .. tab::
+            :tabid: JAVA_SUBJECT_KEY
+      
+            .. include:: /includes/fundamentals/code-snippets/auth-credentials-gssapi-subject-key.rst
 
 By default, the Java driver caches Kerberos tickets by ``MongoClient`` instance.
 If your deployment needs to frequently create and destroy ``MongoClient`` instances, 

source/includes/fundamentals/code-snippets/auth-credentials-gssapi-subject-key.rst

@@ -0,0 +1,9 @@
+.. code-block:: java
+
+   LoginContext loginContext = new LoginContext(<LoginModule implementation from JAAS config>);
+   loginContext.login();
+   Subject subject = loginContext.getSubject();
+
+   MongoCredential credential = MongoCredential.createGSSAPICredential(<username>);
+   credential = credential.withMechanismProperty(MongoCredential.JAVA_SUBJECT_KEY, subject);
+