Filter the headers when redirecting

[seanmonstar]

Some headers should be removed when redirecting to a different domain:

• Cookie
• Authorization

[steverob]

@seanmonstar can I work on this? Rust beginner here :)

[seanmonstar]

Definitely! All issues can always be worked on.

[steverob]

@seanmonstar yay. I'll jump in right away.

[steverob]

@seanmonstar I went through the code and I guess I'll need to call some headers.remove in this part of the client.rs - https://github.com/seanmonstar/reqwest/blob/master/src/client.rs#L308 after checking if we're being sent to a different domain. Is that okay?

Also, I'm wondering how we can write tests for this as the $HOST is always 127.0.0.1:PORT. Any pointers on how I can proceed here? Thanks :)

[seanmonstar]

Yes, definitely, headers.remove is the correct thing to do.

For the tests, I suppose we would just want to unit tests in client.rs. With the addition of proxies (from #30), we could easily setup some proxies that still connect to the localhost server while seeming like different domains...