asp.net-web-api ASP.NET WEB API CORS Enabling Configure CORS for WebAPI 2 with Windows Authentication

Example

The following server-side configuration allows CORS request to work along with Windows Authentication (no anonymous must be enabled in IIS).

web.config - allow unauthenticated (anonymous) preflight requests (OPTIONS)

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

global.asax.cs - properly reply with headers that allow caller from another domain to receive data

protected void Application_AuthenticateRequest(object sender, EventArgs e)
{
    if (Context.Request.HttpMethod == "OPTIONS")
    {
        if (Context.Request.Headers["Origin"] != null)
            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, MaxDataServiceVersion");
        Context.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
        Context.Response.AddHeader("Access-Control-Allow-Credentials", "true");

        Response.End();
    }
}

CORS enabling

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // all requests are enabled in this example. SupportsCredentials must be here to allow authenticated requests          
        var corsAttr = new EnableCorsAttribute("*", "*", "*") { SupportsCredentials = true };
        config.EnableCors(corsAttr);
    }
}

protected void Application_Start()
{
    GlobalConfiguration.Configure(WebApiConfig.Register);
}