Angular -如何在canActivate中避免多个http调用

import { Injectable } from '@angular/core';
import { CanActivate, Router } from '@angular/router';
import { Observable } from 'rxjs';
import { switchMap } from 'rxjs/operators';
import { AuthService } from './auth.service';

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

  canActivate(): Observable<boolean> {
    return this.authService.checkToken().pipe(
      switchMap((isValid: boolean) => {
        if (isValid) {
          return this.authService.getUserRole();
        } else {
          this.router.navigate(['/login']);
          return Observable.of(false);
        }
      })
    );
  }
}