Add authorization

[secana]

Hi @jonhoo,

I've added optional authorization for the HTTP registry. As with a "push", the "HTTP Authorization" header will be send on a index or crate download request.

Why: For private registry, authorization is not only important for the "push", but for the "pull" of any data, too. Different users can have different rights for crates. Sending an optional authorization header satisfies that need.

As this is my first time modifying Cargo, I'm sure I did a lot of stuff wrong or not optimal, so please let me know, where I can improve the code.

If there is generally no interest in support for authorization and private registries, let me know.

[jonhoo]

Hi! I think it's probably best to try and land just the HTTP protocol registry first, and then add authorization afterwards, rather than trying to add both at the same time. There are a bunch of questions around registry authentication and authorization that I know the cargo team has already thought a bunch about, so I think it shouldn't be folded in here.

Also note that my PR that you've submitted a PR on top of is very much experimental, and is unlikely to land in its current form. Instead, the path forward is first to land rust-lang#8985, and then to modify my experimental implementation on top of that, rather than have it use a pre-fetching phase like it currently utilizes.

[secana]

Hi! Alright, I'll keep an I on #8985. If there is any way I can help in the future with the http registry, I'll be happy do to so!

[Eh2406]

When the http-api is on its way to stabilization, I will be doing a deep dive on the authorization side. It sounds like you have well earned opinions on how that should work. I would love to incorporate your expertise! Can we have a meeting when I start my education on that part? I will be reading the comments on rust-lang/rfcs#2719 so if you want to put your prospective down for posterity that would be a useful place.

[secana]

@Eh2406 Sure, feel free to contact me any time!

[Eh2406]

Someone else has start the conversation. Currently the conversation is at https://internals.rust-lang.org/t/pre-rfc-cargo-alternative-registry-authentication/14794