AngularFireAuth: Cannot read property 'GoogleAuthProvider' of undefined - firebase

Question

I'm trying to do authentication with AngularFire. During ng serve, any attempt to instantiate an auth provider (such as firebase.auth.GoogleAuthProvider) results in a crash. I'm doing the exact same thing as the AngularFireAuth quickstart example. Am I missing something?
My app is quite minimal:
// app.component.ts
import { Component } from "#angular/core";
import { AngularFireAuth } from '#angular/fire/auth';
import { auth } from 'firebase/app';
#Component({...})
export class AppComponent {
constructor(private afAuth: AngularFireAuth) { }
ngOnInit() {
this.afAuth.signInWithRedirect(new auth.GoogleAuthProvider());
}
}
// app.module.ts
import { AngularFireModule } from "#angular/fire";
import { AngularFireAuthModule } from '#angular/fire/auth';
...
#NgModule({
declarations: [AppComponent],
imports: [
AngularFireModule.initializeApp(environment.firebase),
AngularFireAuthModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }
// package.json
"dependencies": {
"#angular/core": "~9.1.4",
"#angular/fire": "^6.0.0-rc.2",
"firebase": "7.14.3",
...
},
I have found this question with a similar problem, but they're not using AngularFire, just plain Firebase. With AngularFire I don't think I'm supposed to manually include the Firebase scripts in my index.html.

Answer 1

I've found the real solution. "angular-auth-firebase" must be passed to initializeApp() when importing the AngularFire module in the app module:
#NgModule({
declarations: [ ... ],
imports: [
AngularFireModule.initializeApp(environment.firebase, "angular-auth-firebase"),
AngularFireAuthModule,
...
],
...
})
export class AppModule { }
Old answer (workaround):
I have found a workaround here. If I simply add import "firebase/auth"; to app.module.ts, everything works, though I'm not sure this should be the permanent fix.