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

This closes #1733

Author: liuml07

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

@@ -1090,8 +1090,8 @@
        Uses the values of fs.s3a.access.key and fs.s3a.secret.key.
     * 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.
     * org.apache.hadoop.fs.s3a.auth.IAMInstanceCredentialsProvider: picks up
        IAM credentials of any EC2 VM or AWS container in which the process is running.
   </description>

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

@@ -537,8 +537,8 @@ This means that the default S3A authentication chain can be defined as
        Uses the values of fs.s3a.access.key and fs.s3a.secret.key.
     * 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.
     * org.apache.hadoop.fs.s3a.auth.IAMInstanceCredentialsProvider: picks up
        IAM credentials of any EC2 VM or AWS container in which the process is running.
   </description>