Provide better support for Google Cloud native environments

[samos123]

Is your feature request related to a problem? Please describe.
When you run on Google Cloud, you often can rely on the default application credentials. So there isn't a need to store the private key in an environment variable. Instead it would be preferred to load the firebase admin using this code:

var admin = require('firebase-admin');
var app = admin.initializeApp();

For reference see: https://firebase.google.com/docs/admin/setup

Describe the solution you'd like and how you'd implement it
Change the behaviour such that when no firebaseAdminInitConfig is specified it will initialize the app using the following code:

admin.initializeApp()

Is this a breaking change?
Would this require existing users to change how they're using next-firebase-auth?
It wouldn't be a breaking change because existing users that have the firebaseAdminConfig will continue to work as is

I will happily provide a PR for this change if this is something that you would accept.

[kmjennison]

This makes sense. However, I'd like to also preserve the error for the users who accidentally don't provide any credentials. Ideally:

• If the user provided a credential, init as we currently do.
• If the user did not provide a credential, try admin.initializeApp(). If it fails because of an invalid or missing app credential, throw the existing error (If not initializing the Firebase admin SDK elsewhere, you must provide "firebaseAdminInitConfig" to next-firebase-auth.) I'm not sure what error code the admin app uses for a failed init.

Just FYI, as a fairly straightforward workaround, you can initialize Firebase yourself before initializing next-firebase-auth. See the pattern here.

[samos123]

I tried the latest version and this was working out of the box now when setting useFirebaseAdminDefaultCredential: true,. Thank you for the great library and making it work easily on GCP environments!

[kmjennison]

Wonderful, thanks for the follow-up and kind words!