Consider deferring authentication to another crate

[djc]

I've used (and contributed to) the gcp_auth crate, which IMO is a pretty nice and simple way to deal with authentication/authorization for GCP. Maybe it would be nice to keep this crate focused on specific Cloud Storage APIs and integrate with it (or another existing crate) for authn/authz?

[ThouCheese]

Right that sounds feasible. As a contributor, do you have an idea about how we could best integrate such a library?

[djc]

I noticed that it's not completely straightforward because you need access to a service account's private key, so the gcp_auth API would likely need to be extended somehow. Meanwhile, we found some issues with large uploads (larger than 1 GB) in this library, and I think we will switch to using tonic to call gRPC APIs directly.

[djc]

I think djc/gcp_auth#49 provides the necessary interfaces so that you could use it for authentication and for signing (with a much simpler interface).