Add support for custom maven repositories with credentials

In our custom instance we would like to add a maven repository which requires credentials.

For maven projects, this works because the user can define the credentials in ~/.m2/settings.xml while referencing the maven repository-id.

For gradle projects this doesn’t work. The gradle-way to accomplish this, looks like this:

maven {
       url 'https://artifacts.mycompany.com/snapshots'
       credentials {
                username property("com.mycompany.artifacts.username")
                password property("com.mycompany.artifacts.password")
        }
}

This is currently not supported by Initializr.

[tgeens]

My proposal:

1. Add a credentials field to the MavenRepository model. The type would be a MavenRepositoryCredentials object with username & password fields. (Or a key-value map-like object, which would facilitate extending this to non-basic-auth later on.)

2a. The maven-build-writer can ignore the credentials field - just like the gradle-build-writer is ignoring the name and snapshotsEnabled fields from MavenRepository

2b. The gradle-build-writer can check if there are (non-default) credentials provided and write those to the build.gradle if necessary. Currently the gradle-build-writer can only write repositories on a single line (like maven { url 'https://repo.spring.io/snapshot' }).

To support a representation which includes credentials info, the implementation of GradleBuildWriter#writeRepositories should be updated and the method signature

protected abstract String repositoryAsString(MavenRepository repository)

should change into something that can (optionally) write multi-line repository information, like

protected void writeRepository(IndentingWriter writer, MavenRepository repository)

[wilkinsona]

We hope to address it at some point, that’s why the issue has not be closed. We don’t have any firm plans or a date in mind at the moment, however.