auth.guard.ts

export class AuthGuard implements CanActivate {
  constructor(private authService: AuthService, private router: Router) {
  }

  canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
      if(this.authService.isAuthenticated()) {
        return true;
      }

      this.router.navigate(['/login'], { queryParams: { returnUrl: state.url } });
      return false;
  }
}