Some registries (like Azure Artifact) can require you to authenticate
separately for every package URL if you do not authenticate for the
/simple endpoint. These changes make the auth middleware aware of index
URL endpoints and attempts to fetch keyring credentials for such an
index URL when making a request to any URL it's a prefix of.
The current uv behavior is to cache credentials either at the request
URL or realm level. But with these changes, we also need to cache
credentials at the index level. Note that when uv does not detect an
index URL for a request URL, it will continue to apply the old behavior.
Addresses part of #4056Closes#4583Closes#11236Closes#11391Closes#11507
Previously, we required a username to perform a fetch from the keyring
because the `keyring` CLI only supported fetching password for a given
service and username. Unfortunately, this is different from the keyring
Python API which supported fetching a username _and_ password for a
given service. We can't (easily) use the Python API because we don't
expect `keyring` to be installed in a specific environment during
network requests. This means that we did not have parity with `pip`.
Way back in https://github.com/jaraco/keyring/pull/678 we got a `--mode
creds` flag added to `keyring`'s CLI which supports parity with the
Python API. Since `keyring` is expensive to invoke and we cannot be
certain that users are on the latest version of keyring, we've not added
support for invoking keyring with this flag. However, now that we have a
mode that says authentication is _required_ for an index (#11896), we
might as well _try_ to invoke keyring with `--mode creds` when there is
no username. This will address use-cases where the username is
non-constant and move us closer to `pip` parity.
When trying to upload without a password but with the keyring, check
that the keyring has a password for the upload URL and username and warn
if it doesn't.
Fixes#8781
