Firebase Authentication : Lookup a user by Email

Question

I am using Firebase Authentication with Email and Password

I would like to know if i can 'lookup' a user by email only while also not being signed in as a user

The reason I'd like to do this is, is to simply identify if I am already a user of the system, using an email address only

I looked at this older thread but it appears to be the previous version of Firebase

Is it possible to do this in the current Firebase, or my alternative would be to keep this information available (and open to all?) to find out if a given email is part of my system?

Answer 1

I use fetchProvidersForEmail(email) and if the result return as empty array then, this email hasn't been use to sign up.

firebase.auth().fetchProvidersForEmail(email)
.then(providers => {
  if (providers.length === 0) {
    // this email hasn't signed up yet
  } else {
    // has signed up
  }
});

Answer 2

You can look up user information by email:

firebase.auth().getUserByEmail(email)
  .then(function(userRecord) {
    // See the UserRecord reference doc for the contents of userRecord.
    console.log('Successfully fetched user data:', userRecord.toJSON());
  })
  .catch(function(error) {
   console.log('Error fetching user data:', error);
  });

I'd like to make things more clear that this method does not exist — one could be looking for it in the firebase client library, in which it has never been available in the first place and it wouldn't be a good idea to have anyway. This method is part of the admin SDK, so in order to call the method, you need to run it on the server, and invoke it from the client. OP didn't scope the question to firebase client library, so my answer is still correct.

Retrieve user data

Answer 3

As for today 2021 Nov. 18th, there is no way provided by the Firebase SDK to fetch a user by email.

Answer 4

Server side option:

https://cloud.google.com/identity-platform/docs/reference/rest/v1/projects.accounts/lookup

POST https://identitytoolkit.googleapis.com/v1/projects/{targetProjectId}/accounts:lookup

{ "email": ["[email protected]"] }