[gradle] Where to put Gradle configuration (i.e. credentials) that should not be committed?

First answer is still valid, but the API has changed in the past. Since my edit there wasn't accepted I post it as separate answer.

The method authentication() is only used to provide the authentication method (e.g. Basic) but not any credentials.

You also shouldn't use it since it's printing the credentials plain on failure!

This his how it should look like in your build.gradle

    maven {
        credentials {
            username "$mavenUser"
            password "$mavenPassword"
        }
        url 'https://maven.yourcorp.net/'
   }

In gradle.properties in your userhome dir put:

mavenUser=admin
mavenPassword=admin123

Also ensure that the GRADLE_USER_HOME is set to ~/.gradle otherwise the properties file there won't be resolved.

See also:

https://docs.gradle.org/current/userguide/build_environment.html

and

https://docs.gradle.org/current/userguide/dependency_management.html (23.6.4.1)