Credentials for multiple hosts.

[fa7ca7]

Now cargo login stores a token per host.
If the host parameter is omitted cargo stores a token as default, i.e. as a token for crates.io.

Resolves #3365.
Implemented based on the conversation in #3978.
This RP could be postponed until the cargo team decides which format for registry we should use. Currently, it's a URL.

[rust-highfive]

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[alexcrichton]

This seems related to #4208 where the choice of url here is not the best today (e.g. the index everywhere) but rather we should find a better identifier for this. In that sense this may not be able to land for awhile unfortunately :(

[fa7ca7]

Let me know when I can update this PR accordingly to a new identifier.

[bors]

☔ The latest upstream changes (presumably #4433) made this pull request unmergeable. Please resolve the merge conflicts.

[jan-hudec]

It would also occasionally be useful to read .cargo/credentials from current directory or it's parents the same way as .cargo/config is searched. For example if I had projects for two different customers (or work and private), I might use two different GitHub accounts to keep them separate. And then I might have /home/me/customer1/.cargo/config and /home/me/customer2/.cargo/config. But it appears not to be currently possible to have corresponding .cargo/credentials.

Also, note that (at least unless I am misunderstanding the code), the set of places where config and credentials are searched is actually disjoint. Say I have the project (on Windows this is rather common) in d:\projects\name. The cargo will look for config in d:\projects\name\.cargo\config, d:\projects\.cargo\config and d:\.cargo\config, but as far as I can tell, not c:\Users\me\.cargo\config. But it will only look for credentials in c:\Users\me\.cargo\credentials. Is this split really desired?

[fa7ca7]

This split is really desired. $CARGO_HOME/credentials file is global and should handle all cargo related credentials.

[jan-hudec]

Normally it should. That still does not explain why it must.

[carols10cents]

This PR is kind of stale at this point and needs further changes as discussed, so I'm going to close it. Please open a new PR for updated changes! Thank you!

[bors]

☔ The latest upstream changes (presumably #5907) made this pull request unmergeable. Please resolve the merge conflicts.