angular如何为模板驱动表单的交叉字段验证编写指令

import { Directive } from '@angular/core';
import { NG_VALIDATORS, Validator, AbstractControl, ValidationErrors } from '@angular/forms';

@Directive({
  selector: '[appMatch]',
  providers: [{ provide: NG_VALIDATORS, useExisting: MatchValidatorDirective, multi: true }]
})
export class MatchValidatorDirective implements Validator {
  constructor() {}

  validate(control: AbstractControl): ValidationErrors | null {
    const value = control.value;
    const keys = Object.keys(value);
    const firstKey = keys[0];
    const secondKey = keys[1];

    if (value[firstKey] !== value[secondKey]) {
      return { match: true };
    }
    return null;
  }
}

<form #form="ngForm">
  <input type="password" name="password" [(ngModel)]="user.password" required>
  <input type="password" name="confirmPassword" [(ngModel)]="user.confirmPassword" appMatch [formControl]="form.controls['password']" required>
  <div *ngIf="form.controls['confirmPassword'].errors?.match">
    Passwords do not match.
  </div>
</form>