It would be nice to have the option to specify the location of the auth.json.

In our case we have a repository with a ./composer.json that provides tools to build and deploy the application and a src/composer.json that installs the dependencies of the actual software which has its code source in src/.

We need to install modules that require authentication in both ./ and src/ and therefor it would be awesome to have the possibility to use the src/auth.json in the root ./composer.json as well.

Maybe it could be useful for some users to specify multiple paths. We should still respect the user's {home}/auth.json and the auth.json at the same path as the currently evaluated composer.json.

A config example could be:

{
    "config": {
        "auth-files": [
            "src/auth.json",
            "../auth.json",
            "vendor/my/package/auth.json"
        ]
    }
}