Add more flexibility to authorization unique identifier expectations

[rbclark]

The current code just assumes the unique identifier responds to client ID and issuer. That is currently the case however it is potentially a flawed assumption with new authentication methods being added going forward.

Description

I am currently working to add support to the googleauth library for Workload Identity Federation. As part of this, I am adding a new type of authentication to the googleauth library itself. It is currently assumed that the authorization responds to client_id and issuer, and if either of these are not present then train exits with a stacktrace. This small changes makes train more flexible regarding the authorization object.

Related Issue

https://github.com/googleapis/google-auth-library-ruby/issues/354

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New content (non-breaking change)
• [ ] Breaking change (a content change which would break existing functionality or processes)

Checklist:

• [x] I have read the CONTRIBUTING document.

[chef-expeditor[bot]]

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[rbclark]

Sorry to be a bother but would it be possible for someone to take a look at this and let me know if it needs any changes?