Support authentication for plugin repositories

[jb-2020]

In gradle/gradle-build-action#933 the gradle configurations were enhanced to support a custom plugin repository provided by the user. These plugin repositories can require authentication but there is currently no mechanism to also provide a credentials block to this configuration.

It would be helpful if we could also provide a username and password to the custom plugin repository e.g.

  repositories {
    maven { 
      url "<private gradle plugin repository>
      credentials {
        username = System.getenv("USERNAME")
        password = System.getenv("PASSWORD")
      }
    }
  }

[bigdaz]

Yep, this makes sense. Would you be willing to develop, test and submit a fix?
The implementation should be a pretty simple change to this file, but I don't have an environment to easily test this functionality.

[jb-2020]

@bigdaz I did attempt this a while back and I couldn't seem to use the the project credentials: e.g.

    val user: String by project
    val password: String by project

I think I'm misunderstanding the startup behavior of gradle and these 'init' scripts, the behavior is different than our typical method of gradle configuration. The only work around I found was to reference environment variables directly.

[bigdaz]

You won't be able to access the project instance from within the init-script. The script is loaded very early well before any project is loaded.

Just a thought: before trying to modify the init-script to load 2 new environment variables, can you try using a repository URL like:
https://user:password@repo.mycompany.com?
This is a valid URL format, but I'm not certain if Gradle will translate it to the correct AUTH headers.

[bigdaz]

Fixed in #61

[bigdaz]

Also fixed in 7b589d9