我的标题为http post错误中的空角度6

Question

Hello I am using Angular 6 and I am trying to a http post.

I know the user is allowing Multiple origins with the

    <httpProtocol> <customHeaders> <add name="Access-Control-Allow-Origin" value="*"/> </customHeaders>

my code:

     let data = this.http.post(
            this.base_url + this.walletControllerSubUrl +"login", 
           {username: "exampleuser", password: "Pass123!"}
          );
          data.subscribe(data => console.log(data));
            console.log("data" + data);
            return data;

I always get the error:

" Response to preflight request doesn't pass access control check: The 'Access-Control-Allow-Origin' header contains multiple values ' http://localhost:8100 , *', but only one is allowed"

but I also now noticed that my header seems to go null

    headers: Object { normalizedNames: Map(0), lazyUpdate: null, headers: Map(0) }

what would cause the header to be null when I not even passing any header?

There is another application but in AngularJS, running well with the same post.

what would cause this?

Answer 1

最近我有同样的错误，只需添加proxy.json文件，其中包含定义服务器真实代理的json并将其添加到启动脚本

Answer 2

Modern browsers using CORS will attempt to send a pre-flight request, usually an OPTIONS call. It expects a response from the server with the Access-Control-Allow-Origin header in the response; however, compliance standards restrict this response header to contain only one url in that header (or the wildcard *).

The server you are hitting appears to be sending multiple values.

You'll need to fix the server response to only send back the wildcard or make your request through a proxy.

EDIT: Your headers are null because headers are not sent with the pre-flight request unless the withCredentials requestOptions are used.