AWS IAM Authentication Support

[ericdahl]

Is your feature request related to a problem? Please describe.

With AWS MSK, we use the IAM Authentication mechanism (documented here). It would be great it we could leverage this directly - rather than needing to add additional authentication mechanisms

Describe the solution you'd like simple config options to enable this, enabling sasl_mechanism='OAUTHBEARER' and the minimal required parameters (AWS region). It should search for AWS credentials automatically via the AWS SDK (so there may be no need to have any parameters around this, if assuming standard conventions)