[BUG] Publishing can not handle auth_tokens for base urls

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

I have multiple private npm registries with the same url base.
For installing my packages, it is enough to just specify authentication using this one line in my .npmrc: //<base_url>/:_authToken=<auth_token>.
The parsing of authentication for installing is implemented in npm-registry-fetch/lib/auth.js#regKeyFromUri.

However, this authentication configuration doesn't work for publishing. For publishing, I need to add one line per private registry: //<base_url>/<registry_name>/:_authToken=<auth_token>.
The parsing of authentication for publishing is implemented in @npmcli/config/lib/index.js#Config.getCredentialsByURI.

Expected Behavior

I expect publishing to use the same authentication config as installing.
Specifying an authtoken for just the base url should be enough.

Steps To Reproduce

1. Have a private npm registry (easy to set up using verdaccio, artifactory or gitlab for example)
2. Publish a package to that registry.
3. Clear your .npmrc file and put //<base_url>/:_authToken=<auth_token> in there with <base_url> not being the full registry url (cut off after a /) and <auth_token> being your auth token for that registry.
4. Pull that package in
5. Now update the package's version and try to publish it again
6. See that you get a ENEEDAUTH error

Environment

• npm: 8.10.0
• Node.js: 14.17.0
• OS Name: Windows
• System Model Name: Windows 10
• npm config:

; copy and paste output from `npm config ls` here

Start by comparing npm-registry-fetch/lib/auth.js#regKeyFromUri with @npmcli/config/lib/index.js#Config.getCredentialsByURI, using the reported base-URL auth configuration and publishing reproduction. Trace how credentials are selected for publishing and verify that a token configured at the base URL is accepted without an ENEEDAUTH error.