1. 在 Angular 的 app.module.ts 文件中导入 HttpClientModule：

import { HttpClientModule } from '@angular/common/http';

@NgModule({
  imports: [
    BrowserModule,
    HttpClientModule
  ],
  ...
})
export class AppModule { }

2. 在 Angular 的服务文件中发送 POST 请求并在请求头中添加 'Content-Type': 'application/json'，同时将 responseType 设置为 'text'：

import { HttpClient, HttpHeaders } from '@angular/common/http';

@Injectable({
  providedIn: 'root'
})
export class GithubAuthService {

  private scopes = ['user', 'repo'];
  private clientId = 'YOUR_CLIENT_ID';
  private clientSecret = 'YOUR_CLIENT_SECRET';
  private redirectUri = 'http://localhost:4200/auth/callback';

  constructor(private http: HttpClient) {}

  requestAccessToken(code: string): Observable {

    const headers = new HttpHeaders({
      'Content-Type': 'application/json'
    });

    const body = {
      code,
      client_id: this.clientId,
      client_secret: this.clientSecret
    };

    return this.http.post('https://github.com/login/oauth/access_token',
      JSON.stringify(body), { headers, responseType: 'text' });
  }
}

3. 在 Github 的 OAuth 应用设置中添加重定向 URI。在本例中为 'http://localhost:4200/auth/callback'。

4. 在 Angular 应用中添加一个 callback 页面来接收 Github 返回的 code。本例中为 'http://localhost:4200/auth/callback'。

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { GithubAuthService } from '../github-auth.service';

@Component({
  selector: 'app-auth-callback',
  template: '
',
})
export class AuthCallbackComponent implements OnInit {

  constructor(private route: ActivatedRoute,
              private githubAuthService: GithubAuthService) {}

  ngOnInit() {
    this.route.queryParams.subscribe(params => {
      const code = params['code'];

      this.githubAuthService.requestAccessToken(code).subscribe(response => {
        const token = this.extractToken(response);
        localStorage.setItem('access_token', token);
      });
    });
  }

  private extractToken(body: string): string {
    const matches = body.match(/access_token=(.*?)&/);
    return matches ? matches[1] : null;
  }
}