强制提交参数为特定类型

Question

我有一个使用FormGroup构建的表单。

  <form [formGroup]="signInForm"
        (ngSubmit)="onSubmit(signInForm.value)"
        class="ui form attached fluid">
    <div class="field">
      <div class="ui big left icon input">
        <input type="text"
               placeholder="Username"
               [formControl]="signInForm.controls['username']">
        <i class="user icon"></i>
      </div>
    </div>
    <div class="field">
      <div class="ui big left icon input">
        <input placeholder="Password"
               type="password"
               [formControl]="signInForm.controls['password']">
        <i class="lock icon"></i>
      </div>
    </div>
    <button type="submit" class="big fluid ui blue submit button" disabled>Sign In</button>
  </form>

组件类如下所示：

import {Component, OnInit} from '@angular/core';
import {FormBuilder, FormGroup} from '@angular/forms';

@Component({
  selector: 'app-sign-in',
  templateUrl: './sign-in.component.html',
  styleUrls: ['./sign-in.component.css']
})
export class SignInComponent implements OnInit {

  signInForm: FormGroup;

  constructor(fb: FormBuilder) {

    this.signInForm = fb.group({
      'username': [],
      'password': []
    });

  }

  ngOnInit() {
  }

  onSubmit(value: object): void {
    console.log('you submitted value:', value['username']);
  }

}

考虑value方法上的onSubmit参数，它具有对象类型 我的问题是，我可以为参数value指定一个类型，例如具有特定属性的类SignIn吗？