Fix Private package credentials bug aka the FontAwesome bug

[crubier]

What's the problem this PR addresses?

#601
...

How did you fix it?

Tried to follow instructions in #601 (comment) , but with no experience on the yarn codebase and no comments in the code, I have pretty much no idea what I am doing 🔥 :this-is-fine: :cat_coding:

[arcanis]

Good start! The subtlety in this fix is that the registry is automatically added in npmHttpUtils, cf here:

https://github.com/yarnpkg/berry/blob/master/packages/plugin-npm/sources/npmHttpUtils.ts#L50

If the URL is absolute, it will be problematic as the default registry will be prepended to the URL. At the same time, we want to obtain the right registry information from the absolute URL so that we can extract its configuration, including the credentials.

So what you need to do is implement in npmHttpUtils support for absolute URLs by splitting them into registry and pathname components, based on the registries configured in the project (npmRegistries).

And of course we'll need a test, which involves modifying the mock server (cf test.ts in pkg-tests-core).

[arcanis]

Closing as duplicate of #622 (which is now in master 🎉)