Kindly add permission troubleshooting tips

[holyjak]

Hello! It would be awesome if the Readme could be extended with troubleshooting tips for permissions. I will provide two examples where I lost quite a while due to this.

Example 1: Bad keys

I have reused existing aws creds setup we had already for ECR

  aws-credentials: &aws-credentials
    aws_access_key_id:     ((dev-access-key))
    aws_secret_access_key: ((dev-secret-key))
    aws_session_token:     ((dev-session-token))
    region_name:       "eu-west-1"
# ...
  - name: builds-bucket
    type: s3
    source:
      bucket: my-bucket
      <<: *aws-credentials
      # ...

not noticing that S3 uses different keys. While get succeeded, put failed with

AccessDenied: Anonymous users cannot initiate multipart uploads. Please authenticate. status code: 403

Example 2: Missing token due to a typo

I fixed the keys but made a typo, forgetting a ):

  aws-credentials-s3: &aws-credentials-s3
    access_key_id:     ((dev-access-key))
    secret_access_key: ((dev-secret-key))
    session_token:     ((dev-session-token) # <----
    region_name:       "eu-west-1"

Not it failed with clear but for my puzzling

InvalidToken: The provided token is malformed or otherwise invalid. status code: 400

What would have helped me

I can fly -t myteam hijack -job=mypipeline/myjob and enter the S3 Docker for put but what next?

• How can I see what credentials were supplied to the task? (in Don't hardcode AWS region #1 those would be empty, in Support S3 compatible / custom endpoint URL? #2 token would be ((dev-session-token) instead of the expected value) I do not have them since they come from Concourse variables (which I could likely look up in AWS Secrets Manager or where we have them), moreover I also need to see that they were passed correctly to the S3 resource
• How can I manually check whether access to the bucket is allowed? I guess I could issue a few commands (which?) to install awscli and use that manually to try to upload - but again I'd need the credentials

Thank you!!!