Handling Expired Token From Api in Angular 4

Question

I need help in handling expired token in my angular application. My api has the expired time but my problem is when i forgot to log out of my angular application, after some time, i still can access the homepage but without data. Is there something i can do about this? Are there libraries that can handle this? or are there something i could install? Better, if i nothing will be installed. Here's my authentication code below? Can i add anything that can handle expiration and I won't be able to access the homepage if it expires.

auth.service.ts

 export class AuthService {
  private loggedIn = false;

  constructor(private httpClient: HttpClient) {
  }

  signinUser(email: string, password: string) {  
    const headers = new HttpHeaders() 
    .set('Content-Type', 'application/json');

    return this.httpClient
    .post(
      'http://sample.com/login', 
       JSON.stringify({ email, password }), 
       { headers: headers }
    )
    .map(
        (response: any) => {
          localStorage.setItem('auth_token', response.token);
          this.loggedIn = true;
          return response;
        });
   }

    isLoggedIn() {
      if (localStorage.getItem('auth_token')) {
        return this.loggedIn = true;
      }
    }

   logout() {
     localStorage.removeItem('auth_token');
     this.loggedIn = false;
    }
}

authguard.ts

@Injectable()
export class AuthGuard implements CanActivate {

  constructor(private router: Router, private authService: AuthService) {}

  canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {

    if (this.authService.isLoggedIn()) {
      // logged in so return true
      return true;
    }

    else {
      // not logged in so redirect to login page with the return url
      this.router.navigate(['signin'])
      return false;
      }
  }
}

Answer 1

You can do this using http interceptors.

intercept(req: HttpRequest<any>, next: HttpHandler) {
  if(!localStorage.getItem('token'))
    return next.handle(req);

  // set headers
  req = req.clone({
    setHeaders: {
      'token': localStorage.getItem('token')
    }
  })

  return next.handle(req).do((event: HttpEvent<any>) => {
    if(event instanceof HttpResponse){
      // if the token is valid
    }
  }, (err: any) => {
    // if the token has expired.
    if(err instanceof HttpErrorResponse){
      if(err.status === 401){
        // this is where you can do anything like navigating
        this.router.navigateByUrl('/login');
      }
    }
  });
}

Here's the full solution