No "Access-Control-Allow-Origin" header is present in certain routes at deployment

Question

I've build a frontend with Angular x.x that picks up the routes of an existing ASP.NET Web API 1.x-Application.

There where some problems with the Authentication as well as the communication with the backend because of which I've implemented the following interceptor on the client side:

Angular-Interceptor for the Credentials:

@Injectable()
export class CredentialsInterceptor implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler):
    Observable<HttpEvent<any>> {

    req = req.clone({
      withCredentials: true
    });

    return next.handle(req);
  }
}

To handle existing CORS-Conflicts I modified the Global.asax like this:

protected void Application_BeginRequest(object sender, EventArgs e)
        {
            string httpOrigin = HttpContext.Current.Request.Params["HTTP_ORIGIN"] ?? HttpContext.Current.Request.Params["ORIGIN"] ?? "*";
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", httpOrigin);
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, X-Token, withCredentials");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Credentials", "true");

            if (HttpContext.Current.Request.HttpMethod == "OPTIONS")
            {
                HttpContext.Current.Response.StatusCode = 200;
                var httpApplication = sender as HttpApplication;
                httpApplication.CompleteRequest();
            }
        }

And the web.config like that:

<system.web>
  <authentication mode="Windows" />
  <authorization>
    <allow verbs="OPTIONS" users="*"/>
    <deny users="?"/>
  </authorization>
</system.web>

<system.webServer>
  <handlers>
      <remove name="WebDAV" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness32" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness64" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
  </handlers>
</system.webServer>

On my local machine the Backend was accessible at localhost:80(with IIS Express) while I've hosted my Angular Application at 192.168.xxx.xx:80 over IIS 10.

In this environment everything worked perfectly fine and I had no problems whatsoever.

The Test-Environment is a Server with Windows Server 2008 R2 and IIS 7.5. For Deep-Link-Usage URL-Rewriter 2 is installed

After building the Backend and Frontend and the deploy to the mentioned environment the Application works as expected besides one big flaw.

The Backend-Address in IIS is *:80, *:8080 etc.

The Frontend-Address in IIS is Server-IP:80

While some routes work as expected some others that worked in the local-setup are producing the following CORS-Issue:

Access to XMLHttpRequest at *route* from origin *origin* has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No "Access-Control-Allow-Origin" header is present on the requested source.

So far I can't find any differences between the controllers which are working and those who do not.

Has anyone an idea what is going on here?

Answer 1

Such a minor thing with so much impact.

I forgot to add <remove name="OPTIONSVerbHandler" /> to the web.config handlers.

Now everything works as expected! Hope it helps someone else.