An implementation of
AwsCredentialsProvider that periodically sends an AssumeRoleRequest to the AWS Security Token Service to maintain short-lived sessions to use for authentication. These sessions are updated using a single calling thread (by default) or asynchronously (if StsCredentialsProvider.BaseBuilder.asyncCredentialUpdateEnabled(Boolean) is set). If the credentials are not successfully updated before expiration, calls to StsCredentialsProvider.resolveCredentials() will block until they are updated successfully. Users of this provider must StsCredentialsProvider.close() it when they are finished using it. This is created using builder(). 
