PYTHON-1052 - Clarify delegated auth example

Author: behackett

doc/examples/authentication.rst

@@ -66,19 +66,20 @@ Delegated Authentication
 ------------------------
 .. versionadded: 2.5
 
-In MongoDB 2.4.x a separate authentication source can be specified.
-This feature was introduced in MongoDB 2.4 and removed in 2.6::
+If your user is defined in one database with a role that gives it
+authorization on a different database use the `source` option to specify
+the database in which the user is defined::
 
  >>> from pymongo import MongoClient
  >>> client = MongoClient('example.com')
- >>> client.the_database.authenticate('user',
- ... 'password',
- ... source='source_database')
+ >>> db = client.the_database
+ >>> db.authenticate('user', 'password', source='source_database')
  True
- >>>
+
+Or the `authSource` URI option::
+
  >>> uri = "mongodb://user:password@example.com/?authSource=source_database"
- >>> client = MongoClient(uri)
- >>>
+ >>> db = MongoClient(uri).the_database
 
 MONGODB-X509
 ------------