DOCSP-50554: Add extra AWS info to OIDC page (#648)

(cherry picked from commit 487132e)

Author: mcmorisi

source/fundamentals/authentication/oidc.txt

@@ -195,6 +195,12 @@ see the corresponding syntax.
             .CreateOidcCredential("k8s")
          var client = new MongoClient(mongoClientSettings);
 
+If your application runs on `Amazon Elastic Kubernetes Service <https://aws.amazon.com/eks/>`__
+(EKS), you must create an ``AWS_WEB_IDENTITY_TOKEN_FILE`` environment variable that points
+to the file containing your OIDC token, in addition to completing
+the preceding Kubernetes OIDC authentication steps. To learn more about authenticating to
+MongoDB from AWS applications, see the :ref:`csharp-authentication-aws` guide.
+
 Custom Callback
 ~~~~~~~~~~~~~~~