Warn if no credentials are in effect for S3

[qc00]

Is your feature request related to a problem? Please describe.
When setting S3 credentials via environment variables, aws_auth=true also has to be set, but there's no explicit information about this.

Describe the solution you'd like
Possibilities:

• Require the URI to have a credential (aws_auth=true or credentials in URI)
• Print a warning if AWS_* environment variables are set but aws_auth is not.

[mehertz]

I've been thinking about this.

Print a warning if AWS_* environment variables are set but aws_auth is not.

They might not be using AWS env vars. I think this is quite hard to do actually.

Maybe we should focus our efforts on standardising the URI instead?

[qc00]

Yeah, I don't want to tightly couple to any AWSSDK-specific stuff, either.

Maybe something like: if no explicit credentials or aws_auth, make a test connection to the bucket.

Maybe we should focus our efforts on standardising the URI instead?

I am not sure that would necessarily help. My understanding of the user's issue is: the library appears to "open" successfully but the first call fails with an opaque error.

[mehertz]

if no explicit credentials or aws_auth, make a test connection to the bucket.

I think that's a good idea. Maybe just HEAD the bucket? Hope that would give a non-200 if you don't have any creds.

[mehertz]

We need to be careful not to let this overload storages though. Would be adding a new request per object creation.