Concurrently creating firebase users of the same email succeeds

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[REQUIRED] Step 2: Describe your environment

Operating System version: MacOS sonoma 14.3
Firebase SDK version: 6.5.0
Firebase Product: auth
Python version: 3.11
Pip version: 23.1.2

Note that I have used other tenants on Google Identity Platform in this gcp project but I scrapped that and went back to the single tenant. This issue is happening on the default firebase tenant. (Sharing this fact in case it somehow affects the outcome)

[REQUIRED] Step 3: Describe the problem

I discovered that my tests for some CRUD functionality were creating duplicate firebase users with the same email which is problematic because we rely on the firebase_admin._auth_utils.EmailAlreadyExistsError to safeguard functionality. This appeared as my webserver API was called to create the same user concurrently and it actually made multiple firebase users.

For context, my firebase project -> authentication -> settings -> user account linking -> link accounts with same email is active.

Steps to reproduce:

Creating a new user with an existing email address succeeds when its ran concurrently. I have tested 3 scenarios:

Create the new user (with existing email) a second after the existing user was created 1.1. I get the firebase_admin._auth_utils.EmailAlreadyExistsError like I expect
Attempt to create 4 users with the same email address using asyncio library to create them quickly 2.1 Returns one created user and fires 3 firebase_admin._auth_utils.EmailAlreadyExistsError like I expect

3. Attempt to create 4 users with the same email address concurrently using ThreadPoolExecutor 3.1 Returns 4 new Firebase users who all share the same email address. Not good.

Calling the auth.get_user_by_email(email) returns the latest firebase user created, when I delete the latest one then the function returns the newest one after that and so on.

I plan to add in concurrency/idempotent protections to my API logic in the mean time as this would cause a mess downstream ( as uncommon as it would occur)

Relevant Code:

This is a rough outline of my tests but in general just call create_user concurrently to hopefully see the same results. I use a Fastapi server so you can ignore some of this extracted code using async where its not needed. This is just to demo the issue. firebase_service.py

import firebase_admin
from firebase_admin import auth
if not firebase_admin._apps:
    firebase_admin.initialize_app()

class FirebaseService:

  # async wrapper
  async def create_user(self, email: str, uid: str | None) -> auth.UserRecord | None:
          """Create a user."""
          try:
              user = auth.create_user(email=email, uid=uid)
              return user
          except Exception as e: 
              logger.exception(f"error creating user {email} : {e}")
              return None

  # non async implementation    
      def create_user_sync(self, email: str, uid: str | None) -> auth.UserRecord | None:
          """Create a user."""
          try:
              user = auth.create_user(email=email, uid=uid)
              return user
          except Exception as e: 
              logger.exception(f"error creating user {email} : {e}")
              return None

test.py

import asyncio

common_email = "email_goes_here"
no_uid = None

async def test_multiple_user_same_email_create_asyncio() -> None:
    """Test multiple user creation with same email with asyncio gather."""
    tasks = []
    for i in range(4):
        tasks.append(asyncio.create_task(firebase_service.create_user(uid=no_uid, email=common_email)))
    results = await asyncio.gather(*tasks)
    logger.info(results) # correctly creates 1 user and raises an error for the rest

async def test_multiple_user_same_email_create_threadpool() -> None:
    """Test multiple user creation with same email concurrently"""
    uid = None

    with ThreadPoolExecutor(max_workers=4) as executor:
        futures = [executor.submit(firebase_service.create_user_sync,common_email, no_uid ) for _ in range(4)]
        results = [future.result() for future in as_completed(futures)]
        logger.info(results) # actually creates 4 users with the same email

if __name__ == "__main__":
    # asyncio.run(test_multiple_user_same_email_create_asyncio())
     # asyncio.run(test_multiple_user_same_email_create_threadpool())

firebase / firebase-admin-python