Document providing credentials in index, index-url, and extra-index-url

[chrahunt]

What's the problem this feature will solve?

Currently the user guide does not mention that basic auth credentials are supported in index, index-url, and extra-index-url. This situation is common in enterprise environments using e.g. devpi, Nexus, or Artifactory.

Describe the solution you'd like

Document that <username> or <username>:<password> are supported in the above arguments (like https://[username[:password]]@pypi.company.com/simple). We should also mention:

• any URL special characters must be percent encoded (and maybe provide an example of doing that e.g. cat password.txt | python3 -c 'import sys; from urllib.parse import quote; print(quote(sys.stdin.read()))').
• percent encoding is only supported as of 10.0.0 (Failure to authenticate private repository when URL-encoded character in password #3236) and URL special characters are not supported in credentials for versions of pip below that
• explicit examples, with at least one case where the username is an email address to demonstrate the encoding of @

The description should mention "username", "password", "credentials", and "authentication" so it is easily found via search and google.

One place this could fit is in a dedicated section above or below Using a Proxy Server in the user guide, with links to it from the description of the arguments in:

• pip wheel
• pip search
• pip download (which should really link to pip wheel or a separate page)

It may be good to mention that the pip configuration file can hold these values so they can be used without exposing the arguments on the command-line.

And examples in

• get-pip.py
• pip install

Alternative Solutions

Each repository manager and company maintains this information in their individual knowledge bases.

Additional context

• Index URLs containing unescaped "@" in username cause "Failed to parse" error in pip 19.2 #6775 (comment)
• Certain passwords fail with Extra-index-url with password in pip.conf #6961

[chrahunt]

Fixed by #7201.