title: AWS s3 bucket policy invalid group principal
body: <p>This is a follow on from <a href="https://stackoverflow.com/questions/17050308/how-can-i-enforce-file-type-uploads-with-an-aws-s3-bucket-policy">How can i enforce file type uploads with an AWS S3 bucket policy</a> </p>
  
  <p>When applying the bucket policy:</p>
  
  <pre><code>{
    "Version":"2008-10-17",
    "Statement": [
      {
        "Sid":"AddPerm",
        "Effect":"Allow",
        "Principal": { "AWS": "arn:aws:iam::111122223333:group/admins" },
        "Action": "s3:PutObject",
        "Resource": "arn:aws:s3:::bucket/*.txt"
      }
    ]
  }
  </code></pre>
  
  <p>The group "admins" definitely exists, but I get the error:
  "Invalid principal in policy - "AWS" : "arn:aws:iam::111122223333:group/admins""</p>
  
  <p>Why is it not recognised?</p>