AWS Single Sign-On (SSO) Provider Support

[skmcgrail]

Adds support for the AWS Single Sign-On (SSO) service by supporting the ability to utilize tokens cached in ~/.aws/sso/cache.

Adds support for the AWS SSO provider in the default credential loading chain.

[bflad]

Thank you so much, @jasdel, @skotambkar, and @skmcgrail ❤️ This is going to make so many people happy.

[sidewinder12s]

That is an understatement.

[BourgoisMickael]

What about NodeJS sdk ???

[josegonzalez]

Does anyone have an example for how to use this when using credentials.NewChainCredentials? I have the following code:

		s.creds = credentials.NewChainCredentials(
			[]credentials.Provider{
				&credentials.EnvProvider{},
				&credentials.SharedCredentialsProvider{},
				&ec2rolecreds.EC2RoleProvider{
					Client: ec2metadata.New(awsSession(s.region)),
				},
			})

		sess := session.New(&aws.Config{
			Credentials: s.creds,
			Region:      &s.region,
		})

Not sure what I need to change to add sso support as a provider above.