[firebase_auth] Web: Getting null access token from Google Sign in

[Levi-Lesches]

Describe the bug
After using package:google_sign_in (on web) to get a GoogleSignInAccount, then using that to get a GoogleSignInAuthentication, I cannot use that authentication as an argument for GoogleAuthProvider.credential. The error I get:

Error: Assertion failed: file:///C:/Users/levi/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth_platform_interface-2.0.0/lib/src/providers/google_auth.dart:81:12
  accessToken != null && idToken != null
  "At least one of ID token and access token is required"

First off, notice how the error says at least one, while the assertion actually checks both. Second, I noticed removing this line allowed me to sign in. For context, the error here is that accessToken is null. I could post this issue for google_sign_in, but since I noticed this assertion doesn't seem to prevent me from actually logging in, I thought I'd post it here instead.

To Reproduce
Here's my code:

/// Signs in the user with Google as the provider. 
static Future<void> signIn() async {
	// THIS WORKS ON WEB, NOT MOBILE
	// 
	// final UserCredential userCred = await auth.signInWithPopup(
	// 	GoogleAuthProvider()
	// );
	// final OAuthCredential credential = userCred.credential as OAuthCredential;
	// print("Successfully signed in");
	// print("  idToken: ${credential.idToken}");   // not null
	// print("  accessToken: ${credential.accessToken}");  // not null

	// THIS WORKS ON MOBILE, NOT WEB
	print("Signing in");

	final GoogleSignInAccount googleAccount = await google.signIn();
	print("Got Google account: $googleAccount");
	if (googleAccount == null) {
		return;
	}

	final GoogleSignInAuthentication googleAuth = 
		await googleAccount.authentication;
	print("Got Google auth: $googleAuth");
	print("  ID TOKEN: ${googleAuth.idToken}");  // not null
	print("  Access Token: ${googleAuth.accessToken}");  // null

	// THIS IS THE LINE THAT FAILS ON WEB
	final GoogleAuthCredential credential = GoogleAuthProvider.credential (
		accessToken: googleAuth.accessToken,
		idToken: googleAuth.idToken
	);

	await auth.signInWithCredential(credential);
}

Expected behavior
Either accessToken should be non-null (as it is using signInWithPopup) or FIrebaseAuth should not check that since I am able to log in and download Firestore data just fine without it.

Additional context
Two things:

1. This project started off as a mobile app, and I'm only now adding web. I have another project which was built mainly for web which works perfectly using the same exact code that fails here. So I'm not really sure if the above code will reproduce the issue.
2. Using FirebaseAuth.signInWithPopup works just fine for web. I don't know why accessToken isn't null there, but the main difference is that using signInWithPopup, I don't need to call GoogleAuthProvider.credential, which has the assertion.

Flutter doctor
Run flutter doctor and paste the output below:

[√] Flutter (Channel beta, 1.20.0, on Microsoft Windows [Version 10.0.18363.1016], locale en-US)
    • Flutter version 1.20.0 at C:\Users\levi\flutter
    • Framework revision 916c3ac648 (3 weeks ago), 2020-08-01 09:01:12 -0700
    • Engine revision d6ee1499c2
    • Dart version 2.9.0 (build 2.9.0-21.10.beta)


[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at C:\Users\levi\AppData\Local\Android\sdk
    • Platform android-29, build-tools 29.0.2
    • Java binary at: C:\Program Files\Android\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 3.5)
    • Android Studio at C:\Program Files\Android
    • Flutter plugin version 42.1.1
    • Dart plugin version 191.8593
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)

[√] Connected device (3 available)
    • SM G950U1 (mobile) • 988861314d554d4f52 • android-arm64  • Android 9 (API 28)
    • Web Server (web)   • web-server         • web-javascript • Flutter Tools
    • Chrome (web)       • chrome             • web-javascript • Google Chrome 84.0.4147.125

• No issues found!

Also, here are my relevant dependencies:

  firebase_auth: ^0.18.0
  google_sign_in: ^4.5.1

[Salakar]

Hey, please update to firebase_auth: ^0.18.0+1 - there was a bug with the assertion that was fixed.

Latest versions can be seen here: https://firebase.flutter.dev/docs/migration/#2-update-firebase-plugins

[Levi-Lesches]

I tested and this works. Thanks for the quick fix!