Factor token provider out into a separate trait

[djc]

I ran into dermesser/yup-oauth2#137. In general, making the authentication/authorization process more explicit in the type system seems like a good idea (in a future PR, the YupAuthorizer and dependency could become optional).

[djc]

My work project is now using a different Authorizer impl instead, based on the gcp_auth crate. It has a more minimal API, which makes it easier to use for our purposes. I could add my (equally optional) gcp_auth-based implementation to this crate as well, if you think that makes sense.

[ErichDonGubler]

It makes me scratch my head that the feature flag actually being evaluated inside of src/ is yup-oauth2, because distinguishing between yup-oauth2 and the newly added yup-authorizer flag seems like a distinction that does more harm than good. hyper-rustls is necessary for code enabled with cfg(feature = "yup-oauth2") to compile, and the compilation failures don't give great diagnostics. This all would get obviated by just checking cfg(feature = yup-authorizer) instead.

Did you have a concrete benefit in mind for using flags this way that I'm not seeing?

[djc]

Did you have a concrete benefit in mind for using flags this way that I'm not seeing?

Not really, I tend to want to use the "smallest" feature guard so that if you add more complex feature dependencies later on, stuff is a little easier. I changed all of the feature guards to yup-authorizer for now.

[djc]

Rebased this on top of current master.

[Xaeroxe]

👏 Nicely done!

I could add my (equally optional) gcp_auth-based implementation to this crate as well, if you think that makes sense.

Yes, I think that makes a lot of sense. It might even be appropriate to make it the default authorizer?

[djc]

Yes, I think that makes a lot of sense. It might even be appropriate to make it the default authorizer?

I'd certainly prefer it!

[Xaeroxe]

Great, let's do that in a follow up PR. I'd like to get this one merged. As for whether or not it should be the default, I'd like to make that choice after I see what data is required to build that authorizer

[djc]

Sounds good to me.