Mapped existing sts caller specified role name
Mapped existing sts caller specified role name

When using a federated user session in conjunction with
the -r role assumption option, some of the fidelity of that
initial session is lost (ex: caller-specified-name from
                         https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_variables.html#principaltable)

This will conditionally check, if a new role is asked to be assumed,
if there is already an existing role specified and if so, it will
pass it through to the new session to allow for easier auditing
of users as they traverse more complex IAM role delegation structures.

kubernetes-sigs/aws-iam-authenticator,kubernetes-sigs/aws-iam-authenticator,kubernetes-sigs/aws-iam-authenticator