Add getFirebaseAuth function

lib/utils/cloud/firebase/getFirebaseAuth.ts

@@ -0,0 +1,29 @@
+// eslint-disable-next-line import/no-unresolved
+import { App as FirebaseApp, ServiceAccount } from 'firebase-admin/app';
+// eslint-disable-next-line import/no-unresolved
+import { type Auth, getAuth } from 'firebase-admin/auth';
+import { GeneralizedSecretData } from 'ergonomic-node/lib/utils/environment/index.js';
+import { getFirebaseApp } from 'ergonomic-node/lib//utils/cloud/firebase/getFirebaseApp.js';
+
+export const getFirebaseAuth = (
+	credentialsOrFirebaseApp:
+		| ServiceAccount
+		| GeneralizedSecretData
+		| FirebaseApp,
+): Auth => {
+	const firebaseApp =
+		'clientEmail' in credentialsOrFirebaseApp &&
+		'privateKey' in credentialsOrFirebaseApp &&
+		'projectId' in credentialsOrFirebaseApp
+			? getFirebaseApp(credentialsOrFirebaseApp)
+			: 'SECRET_CRED_FIREBASE_ADMIN_SERVICE_ACCOUNT_CLIENT_EMAIL' in
+					credentialsOrFirebaseApp &&
+			  'SECRET_CRED_FIREBASE_ADMIN_SERVICE_ACCOUNT_PRIVATE_KEY' in
+					credentialsOrFirebaseApp &&
+			  'SECRET_CRED_FIREBASE_ADMIN_SERVICE_ACCOUNT_PROJECT_ID' in
+					credentialsOrFirebaseApp
+			? getFirebaseApp(credentialsOrFirebaseApp)
+			: (credentialsOrFirebaseApp as FirebaseApp);
+
+	return getAuth(firebaseApp);
+};

lib/utils/cloud/firebase/index.ts

@@ -1,4 +1,5 @@
 export * from 'ergonomic-node/lib/utils/cloud/firebase/getCloudStorageBucket.js';
 export * from 'ergonomic-node/lib/utils/cloud/firebase/getFirebaseAdminServiceAccount.js';
 export * from 'ergonomic-node/lib/utils/cloud/firebase/getFirebaseApp.js';
+export * from 'ergonomic-node/lib/utils/cloud/firebase/getFirebaseAuth.js';
 export * from 'ergonomic-node/lib/utils/cloud/firebase/getFirestoreDB.js';