Forms驗證與HttpClient

Tool：Visual Studio 2017 15.5.1版
OS：Windows 10
.NET Framework 4.6
ASP.NET Web Forms

叫用Web API驗證失敗產生的錯誤訊息

No MediaTypeFormatter is available to read an object of type 'String' from content with media type 'text/html'.

在ASP.NET Web Form網站中設計Web API，而在ASP.NET Web Form網站啟用Forms驗證：

<authentication mode="Forms">
  <forms loginUrl="login.aspx"></forms>
</authentication>
<authorization>
  <deny users="?"/>
</authorization>

Web API程式如下:

public class MyAPIController : ApiController {
  public string Get( ) {
    return "Hello";
  }
}

若使用HttpClient叫用Web API時，使用以下程式:

HttpClient client = new HttpClient( );
client.BaseAddress = new Uri( "http://localhost:50778/" );
HttpResponseMessage resp = client.GetAsync( "api/MyAPI" ).Result;
string data = null;
if ( resp.IsSuccessStatusCode ) {
  data = resp.Content.ReadAsAsync<string>( ).Result;
}
Response.Write( data );

就會出現錯誤訊息，這是因為驗證的關係

No MediaTypeFormatter is available to read an object of type 'String' from content with media type 'text/html'.

修改用戶端程式如下，問題就可以解決了!

HttpClient client = new HttpClient( new HttpServer( GlobalConfiguration.DefaultHandler ) );
client.BaseAddress = new Uri( "http://localhost:50778/" );
HttpResponseMessage resp = client.GetAsync( "api/MyAPI" ).Result;
string data = null;
if ( resp.IsSuccessStatusCode ) {
  data = resp.Content.ReadAsAsync<string>( ).Result;
}
Response.Write( data );