IIS Intercept Preflight MVC6

Question

I'm trying to enable CORS allowing my angular app to talk to a new MVC6 Web Api.

The "GET" works but "POST" will not because a CORS Preflight is sent first. IIS intercepts this preflight and responds.

In WebApi2 I could stop IIS from intercepting the preflight with the following web.config setting.

<configuration>
  <system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET, HEAD, POST, DEBUG, DELETE, PUT, PATCH, OPTIONS" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>
  </system.webServer>
</configuration>

Then I could interrogate the request and return the headers I wanted for "OPTIONS".

protected void Application_BeginRequest(object sender, EventArgs e)
{
    if (Context.Request.Path.Contains("api/") && Context.Request.HttpMethod == "OPTIONS")
    {
        Context.Response.AddHeader("Access-Control-Allow-Origin", Context.Request.Headers["Origin"]);
        Context.Response.AddHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
        Context.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
        Context.Response.AddHeader("Access-Control-Allow-Credentials", "true");
        Context.Response.End();
    }
}

I'm able to do both of these in the new MVC6 WebApi but for some reason I can't get IIS to stop intercepting the "OPTIONS" preflight.

I'm using this code in the MVC and I believe it works if I can only get IIS to stop intercepting the "OPTIONS" request.

        app.Use(async (httpContext, next) =>
        {
            httpContext.Response.OnSendingHeaders((state) =>
            {

                if (httpContext.Request.Path.Value.Contains("api/") && httpContext.Request.Method == "OPTIONS")
                {
                    httpContext.Response.Headers.Add("Access-Control-Allow-Origin", new[] { httpContext.Request.Headers["Origin"] });
                    httpContext.Response.Headers.Add("Access-Control-Allow-Headers", new[] { "Origin, X-Requested-With, Content-Type, Accept" });
                    httpContext.Response.Headers.Add("Access-Control-Allow-Methods", new[] { "GET, POST, PUT, DELETE, OPTIONS" });
                    httpContext.Response.Headers.Add("Access-Control-Allow-Credentials", new[] { "true" });
                    return;
                }
            }, null);

            await next();

        });

Has anyone dealt with this or have a working example of MVC6 with CORS working?

I've created a repo on GitHub if anyone would like to download and give it a shot. you'll need Visual Studio 2015. https://github.com/robertdunaway/mvc-cors-options-intercept — user3448990, Aug 17 '15 at 19:32
duplicate with http://stackoverflow.com/questions/31976337/mvc6-cors-intercept-preflight — Avlin, Oct 08 '15 at 23:50

score 1 · Answer 1 · answered Oct 08 '15 at 10:59

I would suggest that one working fine:

app.Use(async (context, next) =>
{
    context.Response.Headers.Add("Access-Control-Allow-Origin", "*");
    context.Response.Headers.Add("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
    context.Response.Headers.Add("Access-Control-Allow-Headers", new[] { "Content-Type, x-xsrf-token" });

    if (context.Request.Method == "OPTIONS")
    {
        context.Response.StatusCode = 200;
    }
    else
    {
        await next();
    }
});

IIS Intercept Preflight MVC6

1 Answers1