如何为 angular 5/nodejs 启用 Access-Control-Allow-Origin？

Question

阅读包括“Access-Control-Allow-Origin”在内的许多方法，但没有一个对我有用。

我使用 @angular/common/http 模块和外部 url 作为数据源。 通过尝试获取数据，得到错误： /////........

Failed to load http://accounts.......com/accounts: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:4200' is therefore not allowed access. The response had HTTP status code 503.

account.service.ts：

import { Injectable                    } from '@angular/core';
import { Router                        } from '@angular/router';
import { HttpClient, HttpParams        } from '@angular/common/http';
import { HttpHeaders                   } from '@angular/common/http';

import { Observable                    } from 'rxjs';
import { catchError                    } from 'rxjs/operators';

import { Account                       } from '../models/account';

const baseUrl     : string = 'http://accounts..................com/';
const httpOptions : any    = {
  headers: new HttpHeaders({
    //'Content-Type':  'application/json',
    'Access-Control-Allow-Headers': 'Content-Type',
    'Access-Control-Allow-Methods': 'GET',
    'Access-Control-Allow-Origin': '*'
  })
};

@Injectable()
export class AccountService {
  private isUserLoggedIn;
  private usreName;
  private account : Account;

  constructor(
    private http: HttpClient,
    private router: Router
  ) {}

  logIn (credentials: any): Observable<Account> {
    return this.http.get<Account>(baseUrl + 'accounts');
  }
}

app.module.ts

import { BrowserModule                 } from '@angular/platform-browser';
import { HttpClientModule              } from '@angular/common/http';
import { NgModule                      } from '@angular/core';

import { routing                       } from './routing';
import { AppComponent                  } from './app.component';
import { AppGlobal                     } from './app.global';

import { AccountComponent              } from './components/account/account.component';

@NgModule({
  declarations  : [
    AppComponent,
    AccountComponent,
    ....
  ],
  imports       : [
    routing,
    BrowserModule,
    HttpClientModule,
    CookieModule.forRoot()
  ],
  providers     : [AccountService, AppGlobal],
  bootstrap     : [AppComponent]
})
export class AppModule { }

请帮忙

//////////////尝试修复1

//......
import { HttpHeaders} from '@angular/common/http';
//.......
logIn (credentials: any): Observable<Account> {

    const headers = new HttpHeaders()
      .append('Content-Type', 'application/json')
      .append('Access-Control-Allow-Headers', 'Content-Type')
      .append('Access-Control-Allow-Methods', 'GET')
      .append('Access-Control-Allow-Origin', '*');
    return this.http.get<Account>(baseUrl + 'accounts',  {headers});
}

我仍然收到该错误：

对预检请求的响应未通过访问控制检查：请求的资源上不存在“Access-Control-Allow-Origin”标头。因此，Origin 'http://localhost:4200' 不允许访问。响应的 HTTP 状态代码为 503。

/////////////尝试修复2

proxy.conf.json：

{
  "/api": {
    "target": "http://localhost:4200",
    "secure": false,
    "pathRewrite": {
      "^/api": ""
    },
    "changeOrigin": true,
    "logLevel": "debug"
  }
}

ng 服务 --proxy-config proxy.conf.json

还有错误

Answer 1

**设置标头以允许 Express 中的 CORS 来源**

=> 在 server.js 文件或邮件文件中添加代码。

app.use(function(req, res, next) {
   res.header("Access-Control-Allow-Origin", "*");
   res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
 });

CORS（跨域资源共享）是一项 HTML5 功能，它允许一个站点访问另一个站点的资源，尽管它们位于不同的域名下。

CORS 的 W3C 规范实际上很好地提供了一些简单的响应标头示例，例如密钥标头、Access-Control-Allow-Origin 以及您必须使用这些标头才能在您的设备上启用 CORS网络服务器。

Answer 2

您提到了 webpack-dev-server，它当然可以处理 CORS，因为它在幕后使用 express。在你的 webpack 配置中

devServer: {
  headers: {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, PATCH, OPTIONS",
    "Access-Control-Allow-Headers": "X-Requested-With, content-type, Authorization"
  }
},

Answer 3

Access-Control-Allow-Origin

响应头不是请求头。您必须将此标头添加到您的 resfull（服务器）

Answer 4

如果您使用的是 .NET Api，请将其添加到您的 WebApiConfig.cs 文件中

    public static void Register(HttpConfiguration config)
    {
        var enableCorsAttribute = new EnableCorsAttribute("*",
                                           "Origin, Content-Type, Accept",
                                           "GET, PUT, POST, DELETE, OPTIONS");
        config.EnableCors(enableCorsAttribute);
        // Web API configuration and services
        // Configure Web API to use only bearer token authentication.
        config.SuppressDefaultHostAuthentication();
        config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/v1/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}