Simplify AuthorizeRequest and AsyncAuthorizeRequest traits

[davidpdrsn]

Fixes #190

This changes the AuthorizeRequest and AsyncAuthorizeRequest traits to be quite a bit simpler I think.

Sync

Before: https://github.com/tower-rs/tower-http/blob/master/tower-http/src/auth/async_require_authorization.rs#L234-L269

After

pub trait AuthorizeRequest<B> {
    type ResponseBody;

    fn authorize(
        &mut self,
        request: &mut Request<B>,
    ) -> Result<(), Response<Self::ResponseBody>>;
}

• authorize now returns Result<(), Response>
• Ok(()) means the request was accepted and will be passed on the inner service
• Err(response) means the request couldn't be authorized and the response will be returned without calling the inner service.

Async

Before: https://github.com/tower-rs/tower-http/blob/master/tower-http/src/auth/async_require_authorization.rs#L234-L269

After

pub trait AsyncAuthorizeRequest<B> {
    type RequestBody;
    type ResponseBody: Body;
    type Future: Future<Output = Result<Request<Self::RequestBody>, Response<Self::ResponseBody>>>;

    fn authorize(&mut self, request: Request<B>) -> Self::Future;
}

• authorize now receives an owned request. This allows you to move the request into the future, do some async stuff which yields some data (such as user id from a database), and then save that in a request extension.
• This wouldn't be possible if the future received a &mut Request because it would require GATs.
• Therefore the future must resolve to Result<Request, Response> so the request can be passed on the inner service.
• Authorization is allowed to change the request body type. Might be useful for someone to buffer and parse the request body to consider it for auth. Then one could change the request body from a generic B to http_body::Full.
• This is essentially the same as AsyncPredicate from tower.

[davidpdrsn]

@hamza1311 what do you think?

[ranile]

API looks good. Better than the simple swapping of Option with Result that I suggested

[davidpdrsn]

AuthorizeRequest and AsyncAuthorizeRequest are now also implemented for closures which is quite ergonomic 😊

[Nehliin]

Looks a lot cleaner to me!

[Nehliin]

This is really neat!

[Nehliin]

Great to have this as part of the docs 👍

[Nehliin]

ah forgot to mention this, we can put in the proper pr number here now

[davidpdrsn]

Oh yeah good catch!