Add support for source_profile and role_arn

[JonathanSerafini]

Hello Friends,

This PR adds initial support to aws-sdk-core for nested profiles using source_profile as well as assume role using role_arn when using a .aws/credentials file.

To be honest, I'm not 100% familiar with the various ways that Credentials objects are used within this code base, so I've tried to make this as non-intrusive as possible.

[trevorrowe]

Sorry for the accidental closure. A git commit referenced the wrong issue (998 instead of 988). I haven't looked at this pull request yet. I'll check with @awood45 to see if we can get this looked at.

[JonathanSerafini]

@trevorrowe just out of curiosity, should this have been provided in a different manner ? it's been a month and the only feedback there's been was an accidental close, it makes you feel all warm and fuzzy inside ;)

[agperson]

My use case is very similar and I would love to see movement on this PR!

[agperson]

It's really disappointing that this functionality was not merged.

[JonathanSerafini]

¯_(ツ)_/¯

[trevorrowe]

@agperson @JonathanSerafini Sorry for the radio silence on this issue. This has not been intentional, but I understand why it sucks.

The frank reason why it has taken so long to approve this is that we are collaborating with the other SDK and tool teams on how to best to share configuration. The ~/aws/.credentials file is an important part of this. We receive frequent requests to support additional features available in the CLI and we want to make certain that we can support the same credential loading strategies across all of our tools (Java, .NET, PHP, Ruby, Python, JavaScript, Go-lang, CLI, etc).

I agree this functionality is useful and I would like to merge it. I also would like to ensure that the format and behavior is what we are going to expect moving forward. @awood45 has been reaching out to other SDK maintainers. What we are trying to avoid is a situation where each tool does something different, which is where we find ourselves largely today. We are currently having discussions on how to expand the shared configuration features, especially those around credentials.

Please feel free to re-open the pull request. While we have not merged it, the work is valuable. Our ignoring the pull request was not a good communication strategy. I apologize for this.