Is there any way that I could set custom rules for passwords when a user create an account? It seems like firebase doesn't provide a way to edit the password rules. I know I can set password rules on front end, but just like Frank van Puffelen mentioned, this method can be bypassed by directly calling the API. Is is possible to write some cloud function to handle account-creation request, and reject the request if the password is invalid?
Sure, you can write a Cloud Function to create email/password accounts. You'll need to use the Admin SDK to get a hold of user management APIs.
来源：https://stackoverflow.com/questions/47897741/enforce-custom-rules-for-passwords-for-firebase-auth-accounts