How to wait for firebase auth before starting angular app

Question

I would like to display a small loading logo while the firebase authentication is retrieving a user token, before starting "for real" the single page application.

So far I have an authentication service :

constructor(
    public afAuth: AngularFireAuth,
    ) {
      this.afAuth.onAuthStateChanged(user => {
        if (user) {
           this.setCredentials(user)
        }
      })
    }

  setCredentials(user: firebase.User) {
      return user.getIdTokenResult(true).then(idTokenResult => {
        this.credentials = {
          userId: idTokenResult.claims.id,
          role: idTokenResult.claims.role,
          token: idTokenResult.token,
        };
        // STARTS THE APPLICATION NOW ?
      })
  }

Is it possible to achieve such behavior ? I've read about APP_INITIALIZER without success. I want to avoid localstorage / session storage and instead rely solely on this initialization.

Update :

created an init function :

export function initApp(auth: AuthService, afAuth: AngularFireAuth) {
    return () => {
      return new Promise((resolve) => {
        afAuth.user.pipe(
            take(1),
        ).subscribe(user => {
          if (user) {
            auth.setCredentials(user)
            .then(() => resolve())
          } else {
              resolve();
          }
        })
      });
    }
  }

And edited AppModule providers:

providers: [
    interceptorProviders /* my interceptors */,
    {
      provide: APP_INITIALIZER,
      useFactory: initApp,
      deps: [AuthService, AngularFireAuth],
      multi: true
    }
  ]

Still need to figure out how to add a waiting logo but it's another question. I'll update asap.

Answer 1

Answering to my own question

To summarize I wanted to make sure my token claims (role, and user id per say) associated with a firebase user were stored in my auth service before dealing with routing, because components inside these routes would use those credentials.

In the end I did not follow the APP_INITIALIZER that is not really a good solution.

Auth Service

private _credentials: BehaviorSubject<Credentials> = new BehaviorSubject<Credentials>(null);
public readonly credentials$: Observable<Credentials> = this._credentials.asObservable();

constructor(private afAuth: AngularFireAuth) {
this.afAuth.authState.subscribe(user => {
      this._credentials.next(null);
      if (user) {
        user.getIdTokenResult().then(data => {
          const credentials = {
            role: data.claims.role,
            token: data.token,
            userId: data.claims.userId
          }

          this._credentials.next(credentials);
          console.log(credentials);
        })
      } else {
        this._credentials.next({role: null, token: null, userId: null});
      }
    })
}

get credentials(): Credentials {
    return this._credentials.value;
}

Display a waiting spinner in app.component

Below prevents routes from displaying if credentials not set. In the template :

<div *ngIf="!(credentials$ | async)" class="logged-wrapper">
    <div class="spinner-wrapper">
        <mat-spinner class="spinner"></mat-spinner>
    </div>
</div>
<router-outlet *ngIf="(credentials$ | async)"></router-outlet>

In the component :

credentials$: Observable<any>;

constructor(
    private auth: AuthService,
  ) {
    this.credentials$ = this.auth.credentials$;
  }

Auth Guard

The takewhile allows me to make sure my credentials are set before going further.

canActivate(next: ActivatedRouteSnapshot, state: RouterStateSnapshot):Promise<boolean> {
    return new Promise((resolve) => {
        this.auth.credentials$.pipe(
            takeWhile(credentials => credentials === null),
        ).subscribe({
            complete: () => {
                const credentials = this.auth.credentials
                if (!credentials.role) {
                    this.router.navigate(['/login'], { queryParams: { returnUrl: state.url } })
                    resolve(false);
                }
                if (next.data.roles && next.data.roles.indexOf(credentials.role) === -1) {
                    this.router.navigate(['/']);
                    resolve(false);
                }
                resolve(true)
            }
        })
    })
}