linkWithRedirect does not work with auth emulator

[smousa]

[REQUIRED] Describe your environment

• Operating System version: Ubuntu 20.10
• Browser version: Chromium 87.0.4280.88 snap
• Firebase SDK version: 8.18.0
• Firebase Product: auth emulator

[REQUIRED] Describe the problem

Steps to reproduce:

1. Configure application to connect to Firebase Auth emulator

2. Log into application using "google auth" credentials

3. Unlink "google auth" credentials from the user by calling

   firebase.auth().currentUser.unlink('google.com')

4. Relink "google auth" credentials to the user by calling

const googleProvider = new firebase.auth.GoogleAuthProvider()
firebase.auth().currentUser.linkWithRedirect(googleProvider)

Relevant Code:

// IMPORTANT: make sure you are connected to the emulator!!!

import firebase from 'firebase/app'

const provider = new firebase.auth.GoogleAuthProvider

// This happens out of band
auth.signInWithRedirect(provider)

// I don't think this is exceptional to me unlinking and
// relinking, but just in case...
async function unlinkAndRelink() {
  await firebase.auth().currentUser.unlink('google.com')
  await firebase.auth().currentUser.linkWithRedirect(provider)
}

Results

{"error":{"code":400,"message":"API key not valid. Please pass a valid API key.","errors":[{"message":"API key not valid. Please pass a valid API key.","domain":"global","reason":"badRequest"}],"status":"INVALID_ARGUMENT"}}"

Console: auth.esm.js?b7aa:219 GET https://www.googleapis.com/identitytoolkit/v3/relyingparty/getProjectConfig?key=fake-api-key&cb=1610124371002 400

[rosalyntan]

Thanks for filing this issue! I've filed b/177944015 for internal tracking.