fix: IMDSV2 token should only be fetched if needed

No need to fetch the token if environment variables for both the region and the security credentials have been provided.

Author: amanda-tarafa

aip/auth/4117.md

@@ -240,7 +240,9 @@ The auth libraries and applications **must** follow the steps below:
   **imdsv2_session_token_url** fields if they are provided. The host should
   either be **169.254.169.254** or **fd00:ec2::254**.
 - If **imdsv2_session_token_url** is available, then fetch session token
-  from **imdsv2_session_token_url**.
+  from **imdsv2_session_token_url**. Note: only perform this step if you
+  need to communicate with the metadata server to fetch the region and/or
+  the security credentials
 - Check the environment variables in the following order (`AWS_REGION` and
   then the `AWS_DEFAULT_REGION`) to determine the AWS region. If found, skip
   using the AWS metadata server to determine this value.