Support for user-specified AWS credential providers

[thomascollett]

Adds support for passing in a credentials provider using the s3fs_credentials_provider property.

This is useful if you are assuming a role, which requires refreshable credentials from STS using a STSAssumeRoleSessionCredentialsProvider. This would enable segregation using a separate AWS role per customer, with each role only having permissions to access their own objects in the bucket.

e.g.

STSAssumeRoleSessionCredentialsProvider credentialsProvider = new STSAssumeRoleSessionCredentialsProvider.Builder(
          roleArn,
          "sftp-server")
          .withExternalId("external-id")
          .withRoleSessionDurationSeconds(3600)
          .build();

[carlspring]

Hi @thomascollett ,

I hope you're well!

I'm not sure, if you've recieved my e-mail, but just in case -- I'm reaching out here as well. As this project seems to have been abandoned, I was wondering, if you'd be interested in contributing these fixes against our spin-off (rebranded fork) -- s3fs-nio?

Kind regards,

Martin