会是这样的:

import { CanActivate, Router } from '@angular/router';
import { Injectable } from "@angular/core";
import { AngularFireAuth } from '@angular/fire/auth';
import { take, switchMap } from 'rxjs/operators';

@Injectable()
export class AdminGuard implements CanActivate {

    constructor(private auth: AngularFireAuth, private router: Router) { }

    canActivate() {
        return this.auth.authState.pipe(
            take(1),
            switchMap(async (authState) => {
                if (authState) { // check are user is logged in
                    const token = await authState.getIdTokenResult()
                    if (!token.claims.admin) { // check claims
                        this.router.navigate(['/auth/login'])
                        return false
                    } else {
                        return true
                    }
                } else {
                    this.router.navigate(['/auth/login'])
                    return false
                }
            }),
        )
    }
}