Support adding Authorization HTTP headers through the `RUSTUP_AUTHO…

[amejia1]

…RIZATION_HEADER` environment variable.

This partially addresses #1343 by supporting reverse proxies which require authentication that function as mirrors to https://static.rust-lang.org .

[djc]

If this is about a reverse proxy I don't think the complexity of doing this is worth it. Instead, it seems like the main issue is that we might leak credentials in logging when using RUSTUP_DIST_SERVER, which can be remedied more directly. We should also not unlink #1343 from this, because that issue seems to be about a forward proxy, not a reverse proxy.

[amejia1]

If this is about a reverse proxy I don't think the complexity of doing this is worth it. Instead, it seems like the main issue is that we might leak credentials in logging when using RUSTUP_DIST_SERVER, which can be remedied more directly. We should also not unlink #1343 from this, because that issue seems to be about a forward proxy, not a reverse proxy.

This change would also support token based authentication through the Bearer scheme. I had those in mind when I thought to implement these changes. Here are some examples of what I mean https://api.goauthentik.io/authentication/

[amejia1]

I have converted this PR to a draft. I need to investigate ways to start a forward proxy which requires authentication.