DOCSP-32752 Support for setting AWS region (#958)

* DOCSP-32752 Suppor for setting AWS region

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* default region

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Author: lindseymoore

source/fundamentals/authentication/mechanisms.txt

@@ -228,7 +228,29 @@ The driver checks for your credentials in the following sources in order:
 
          export AWS_WEB_IDENTITY_TOKEN_FILE=<absolute path to file containing your OIDC token>
 
-      After you've set the preceding environment variable, specify the ``MONGODB-AWS``
+      AWS recommends using regional AWS STS endpoints instead of global 
+      endpoints to reduce latency, build-in redundancy, and increase session token validity.
+      To set the AWS region, set `AWS_REGION <https://docs.aws.amazon.com/sdkref/latest/guide/feature-region.html>`__ 
+      and `AWS_STS_REGIONAL_ENDPOINTS <https://docs.aws.amazon.com/sdkref/latest/guide/feature-sts-regionalized-endpoints.html>`__
+      as environment variables, as shown in the following example: 
+
+      .. code-block:: bash
+         
+         export AWS_STS_REGIONAL_ENDPOINTS=regional // Enables regional endpoints
+         export AWS_REGION=us-east-1 // Sets your AWS region
+         
+      If both these environment variables aren't set, the default region is 
+      ``us-east-1``. For a list of available AWS regions, see the
+      `Regional Endpoints <https://docs.aws.amazon.com/general/latest/gr/rande.html#regional-endpoints>`__ 
+      section of the AWS Service Endpoints reference in the AWS documentation. 
+
+      .. warning:: Consult your SDK's Documentation for Setting an AWS Region
+
+         You cannot set your AWS region with environment variables for all SDKs,
+         as in the above example. See your SDK's specific documentation for 
+         configuring an AWS region. 
+
+      After you've set the preceding environment variables, specify the ``MONGODB-AWS``
       authentication mechanism in your connection string as shown in the following example:
 
       .. literalinclude:: /code-snippets/authentication/aws-env-variable.js