enabling cross-origin resource sharing on IIS7

Question

I recently ran into with posting Javascript requests to another domain. By default XHR posting to other domains is not allowed.

Following the instructions from http://enable-cors.org/, I enabled this on the other domain.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
 <system.webServer>
  <httpProtocol>
    <customHeaders>
      <add name="Access-Control-Allow-Origin" value="*" />
      <add name="Access-Control-Allow-Methods" value="GET,PUT,POST,DELETE,OPTIONS" />
      <add name="Access-Control-Allow-Headers" value="Content-Type" />
    </customHeaders>
  </httpProtocol>
 </system.webServer>
</configuration>

Everything works fine now, however it is still return a 405 response before sending back the working 200 response.

Request URL:http://testapi.nottherealsite.com/api/Reporting/RunReport
Request Method:OPTIONS
Status Code:405 Method Not Allowed
Request Headersview source
Accept:*/*
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-GB,en-US;q=0.8,en;q=0.6
Access-Control-Request-Headers:origin, content-type, accept
Access-Control-Request-Method:POST
Connection:keep-alive
Host:testapi.nottherealsite.com
Origin:http://test.nottherealsite.com
Referer:http://test.nottherealsite.com/Reporting
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1
Response Headersview source
Access-Control-Allow-Headers:Content-Type
Access-Control-Allow-Methods:GET,PUT,POST,DELETE,OPTIONS
Access-Control-Allow-Origin:*
Allow:POST
Cache-Control:private
Content-Length:1565
Content-Type:text/html; charset=utf-8
Date:Tue, 18 Sep 2012 14:26:06 GMT
Server:Microsoft-IIS/7.5
X-AspNet-Version:4.0.30319
X-Powered-By:ASP.NET

Update: 3/02/2014

There is a recently updated article in MSDN magazine. Detailing CORS Support in ASP.NET Web API 2.

http://msdn.microsoft.com/en-us/magazine/dn532203.aspx

Answer 1

It is likely a case of IIS 7 'handling' the HTTP OPTIONS response instead of your application specifying it. To determine this, in IIS7,

1. Go to your site's Handler Mappings.

2. Scroll down to 'OPTIONSVerbHandler'.

3. Change the 'ProtocolSupportModule' to 'IsapiHandler'

4. Set the executable: %windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll

Now, your config entries above should kick in when an HTTP OPTIONS verb is sent.

Alternatively you can respond to the HTTP OPTIONS verb in your BeginRequest method.

    protected void Application_BeginRequest(object sender,EventArgs e)
    {
        HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");

        if(HttpContext.Current.Request.HttpMethod == "OPTIONS")
        {
            //These headers are handling the "pre-flight" OPTIONS call sent by the browser
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept");
            HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000" );
            HttpContext.Current.Response.End();
        }

    }