Handle poetry's credentials for alternative repositories

[sinoroc]

The plugin should be able to read the credentials for alternative source repositories as they are configured via poetry config ... and somehow use them in tox.

Related:

• How to define poetry configuration in tox? #8
• Allow download from alternative repositoires without authentication for pip via environment variables #13

[sinoroc]

I guess in a first step we could place the credentials in the URL via pip's environment variables.

Something of note, both pip and poetry seem to delegate to keyring, but probably they do not use the same services. This should be investigated.

[sinoroc]

Maybe of interest:

• https://discuss.python.org/t/adding-a-global-config-to-specify-package-indexes/8599