next-firebase-auth | Simple Firebase authentication for all Next.js rendering | Authentication library

We expect certain sensitive config values to be falsy on the client side (see the config validation code). This is a precaution to make sure developers aren't accidentally bundling something like their Firebase private key with client JS. To fix this, ensure the config setting is undefined on the client side by logging it to your browser console. You can use Next's .env support to set server-only variables. Never use the NEXT_PUBLIC* prefix for any secret values. This package will call a Google endpoint when it needs to refresh a token server-side. You're seeting an error in that request. To fix this, confirm that your firebaseAdminInitConfig.credential.clientEmail is correct. It should be the email paired with your Firebase private key. If that doesn't help, try inspecting the custom token to manually validate the values and structure. Some people encounter this problem when their server time is incorrect. If auth is working on the client side but not on the server-side, the auth cookies are most likely not set. To fix this, confirm the auth cookies are set in your browser's dev tools. If they're not set, please check that the secure, sameSite, and path options passed in the next-firebase-auth config make sense for your environment. For example, if you're testing on non-HTTPS localhost, make sure secure is false. In addition, please double-check your server logs for any errors to ensure the Firebase admin app is initializing properly. Often, this is caused by an incorrect the email in Firebase credentials. Please verify that the email is correct and is from the same Firebase account as your private key, or try generating a new key: https://firebase.google.com/docs/admin/setup. You can try setting up your credentials in the example app to be sure your app code isn't a problem. In local development, try clearing data/cookies for localhost in case you previously signed in with another Firebase account and still have auth cookies signed by another private key. You can also try disabling the Firebase Authentication Emulator. Remove firebaseAuthEmulatorHost from your config and remove FIREBASE_AUTH_EMULATOR_HOST from your .env file. See adding a private key to Vercel and this discussion on private key formatting.