[Feature] Support authorization of multiple requests

[vicsn]

💥 Proposal

We now have a flow to generate all requests in an execution using Stack::sample_authorization. With that in hand, only should be able to then create a complete authorization (i.e. generate all remaining transitions). So authorize_request could:

• take in an array of requests
• be renamed to authorize_requests

For this to be possible we may need to support a new CallStack variant or adjust some evaluate_function logic...

Open question: are there any hypothetical cases where Stack::sample_authorization may fail making it worth to preserve the existing API?

[iamalwaysuncomfortable]

What's the case for this other than multi-party or external signing?

Open question: are there any hypothetical cases where Stack::sample_authorization may fail making it worth to preserve the existing API?

sample_authorization generates random values for input_ids/scm/tcm/tvk/signature, which would allow an authorization struct to be constructed, but it'd ultimately fail checks during subsequent execution. So to the contrary, I don't see how authorizations generate by Stack::sample_authorization would ever succeed at execution time as the checks in Request.verify would almost always fail.

For authorizations being generated by single signers, if we need correctly generated request objects, it seems authorize_unchecked is pretty much doing the best that can be done.

If this feature is being suggested for external or multi-signer use cases, it would probably be helpful to develop utilities which help create the correct request chains.