HADOOP-16735. Make it clearer in config default that EnvironmentVariableCredentialsProvider supports AWS_SESSION_TOKEN. Contributed by Mingliang Liu

This closes #1733

hadoop-common-project/hadoop-common/src/main/resources/core-default.xml

@@ -987,8 +987,8 @@
         fs.s3a.access.key and fs.s3a.secret.key.
     2. com.amazonaws.auth.EnvironmentVariableCredentialsProvider: supports
         configuration of AWS access key ID and secret access key in
-        environment variables named AWS_ACCESS_KEY_ID and
-        AWS_SECRET_ACCESS_KEY, as documented in the AWS SDK.
+        environment variables named AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY,
+        and AWS_SESSION_TOKEN as documented in the AWS SDK.
     3. com.amazonaws.auth.InstanceProfileCredentialsProvider: supports use
         of instance profile credentials if running in an EC2 VM.
   </description>

hadoop-tools/hadoop-aws/src/site/markdown/tools/hadoop-aws/index.md

@@ -289,8 +289,8 @@ of `com.amazonaws.auth.AWSCredentialsProvider` may also be used.
         See also fs.s3a.access.key and fs.s3a.secret.key.
     2. com.amazonaws.auth.EnvironmentVariableCredentialsProvider: supports
         configuration of AWS access key ID and secret access key in
-        environment variables named AWS_ACCESS_KEY_ID and
-        AWS_SECRET_ACCESS_KEY, as documented in the AWS SDK.
+        environment variables named AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY,
+        and AWS_SESSION_TOKEN as documented in the AWS SDK.
     3. com.amazonaws.auth.InstanceProfileCredentialsProvider: supports use
         of instance profile credentials if running in an EC2 VM.
   </description>