initializeAuth is not idempotent

[jhuleatt]

Operating System

n/a

Environment (if applicable)

n/a

Firebase SDK Version

11.6.0

Firebase SDK Product(s)

Auth

Project Tooling

Next.js

Detailed Problem Description

getAuth is idempotent, but initializeAuth is not. This causes issues with hot reloads while editing a Next.js app.

Steps and code to reproduce issue

Use initializeAuth in a Next.js app. Start the dev server, use initializeAuth, and see it error.

[Davileal]

Hey @jhuleatt

After reviewing the source code, I noticed that initializeAuth() is intentionally non-idempotent when different parameters are passed (e.g., a different persistence array or popupRedirectResolver). In those cases, the SDK throws an expected exception to avoid inconsistent Auth behavior:

// packages/auth/src/core/auth/initialize.ts
export function initializeAuth(app: FirebaseApp, deps?: Dependencies): Auth {
  const provider = _getProvider(app, 'auth');

  if (provider.isInitialized()) {
    const auth = provider.getImmediate() as AuthImpl;
    const initialOptions = provider.getOptions() as Dependencies;
    if (deepEqual(initialOptions, deps ?? {})) {
      return auth;
    } else {
      _fail(auth, AuthErrorCode.ALREADY_INITIALIZED);
    }
  }

  const auth = provider.initialize({ options: deps }) as AuthImpl;

  return auth;
}

There are dedicated unit tests confirming this design. For example, this test explicitly verifies that re-calling initializeAuth() with a different persistence order will throw:

// packages/auth/src/core/auth/initialize.test.ts
it('should throw if called again with different params (persistence)', () => {
  initializeAuth(fakeApp, {
    persistence: [inMemoryPersistence, fakeSessionPersistence]
  });
  expect(() =>
    initializeAuth(fakeApp, {
      persistence: [fakeSessionPersistence, inMemoryPersistence]
    })
  ).to.throw();
});

To better understand this, I also created a minimal Next.js app using initializeAuth(), and I only observed the error after changing the configuration parameters (e.g. switching the order of persistence strategies) during a hot reload. If the parameters remain exactly the same, no error occurs. Did the error occur for you even without changing the initializeAuth configuration? I’d be happy to help contribute to that if needed.