Support for web identity token authentication

[AFriemann]

Hey there!

It would be helpful to support web identity token authentication. This would allow using IRSA on EKS (https://docs.aws.amazon.com/emr/latest/EMR-on-EKS-DevelopmentGuide/setting-up-enable-IAM.html) instead of having to rely on outdated strategies like kube2iam or hard-coded user access keys.

Here is an example implementation on the golang sdk: aws/aws-sdk-go@2e1d76a

[palmobar]

Hi, I suppose once this is done supporting sso will be only one step away? This is quite a problem for anyone wanting to deploy theirs elixir/erlang app to EKS.

[onno-vos-dev]

I can try and take a look at this in the next week or two. If need some help from someone else in testing this as O don't currently have the necessary environment setup for it so any volunteers?

[AFriemann]

@onno-vos-dev we could probably support with testing this, we have bigger issues with development capacity :)

[dw-kihara]

I also need support for web identity tokens in my (company's) project, so I am writing a provider.
My work here: dw-kihara#1
Moved here: #73

I think this code is not well-tested (or even well-coded), but I hope it helps.