Allow to add own data to SignedHeaders

[avoidik]

Could you please provide any way how to append something to SignedHeaders?

[DavidMuller]

Hi @avoidik -- can you describe your use case? See also previous PRs (e.g. #11) that have adjusted what is ultimately placed in the SignedHeaders portion of the Authorization header.

[avoidik]

Hi @DavidMuller the use case is Vault and its additional header X-Vault-AWS-IAM-Server-ID

https://github.com/hashicorp/vault/blob/master/builtin/credential/aws/path_login.go#L1412

[avoidik]

PR was added to cover this use-case

[avoidik]

another use-case

This use-case covers optional headers to sign mentioned at
https://docs.aws.amazon.com/general/latest/gr/sigv4-signed-request-examples.html

# Note: The request can include any headers; canonical_headers and
# signed_headers lists those that you want to be included in the 
# hash of the request. "Host" and "x-amz-date" are always required.

[avoidik]

another user-case

https://github.com/kubernetes-sigs/aws-iam-authenticator#api-authorization-from-outside-a-cluster