Currently one needs to use access key ID / secret key to configure S3 datastore support. Commenting these out causes "Unexpected error storing media: invalid configuration: missing s3 options" error raised.

Assuming minio-go has the support (it should, given minio seems to have AssumeRole support), it would be great to allow using S3 at least against AWS without an access key ID / secret key.

https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html