IAM Role support about deb-s3

[jjshoe]

http://docs.aws.amazon.com/AWSRubySDK/latest/AWS/Core/CredentialProviders/AssumeRoleProvider.html

[jjshoe]

The DefaultProvider claims to try this as a fallback in the Ruby SDK docs, but doesn't seem to be the case here.

[twmartin]

@jjshoe - I believe deb-s3 will support authentication through IAM roles. I was running into difficulty during upload attempts before I realized that I needed to allow s3:PutObjectAcl in addition to s3:PutObject in my IAM role policy.

[gaieges]

I've had success with an instance role and a IAM policy behind that being able to upload to s3 using deb-s3.

However, the one piece of feedback I would leave is to ensure that the PutObjectAcl requirement (and in general what a minimum IAM policy is needed for this) is included in documentation. I spent a bit of time trying to figure out what the proper minimum policy needed to allow this to work was, before finding this thread (thanks @twmartin!).