title: python boto3 error: Not authorized to perform assumed role on resource
body: <p>I am trying to move files from a S3 bucket in one account(source account) to S3 bucket in another account(destination account)
  I am using sagemaker notebook so I have a sagemaker role.
  I also have a role in my team account  which has full s3 access and fullsagemaker access and in the trust relationship i have given the destination account role arn and sagemaker role arn.
  The destination account also has my team role arn and sagemaker role arn in its trust policy.</p>
  <p>I am trying to assume my team role and then I will assume the destination role to copy files.</p>
  <pre><code>    import boto3
      sts_client = boto3.client('sts')
  assumed_teamrole_object = sts_client.assume_role(DurationSeconds=1800,
                                                   RoleArn='myteamrole',
                                                   RoleSessionName='test1')
      assumed_destrole_object = sts_client.assume_role(DurationSeconds=1800,
                                                   ExternalId='externalid provided by destination account',
                                                   RoleArn='destination account role',
                                                   RoleSessionName='test2')
  </code></pre>
  <p>The first three lines execute fine. when I try to assume the destination role i am getting the error</p>
  <p><strong>An error occurred (AccessDenied) when calling the AssumeRole operation: User: arn:aws:sts::role/AmazonSageMaker-ExecutionRole-/SageMaker is not authorized to perform: sts:AssumeRole on resource: arn:aws:iam::destinationrole</strong></p>
  <p>Is there something I am missing, what am i doing wrong. Please help.
  I dont have any user , it is just roles</p>
  <p>Thanks!</p>