Intercept HTTP OPTIONS before windows authentication ASP.NET Core 2.0

Question

how to intercept an http options request (Cors Preflight) before the windows authentication of IIS ?

I make a middleware and i tryed this :

 public async Task Invoke(HttpContext context)
    {
        if (context.Request.Method.Equals("OPTIONS"))
        {
            context.Response.StatusCode = 204;
            context.Response.Headers.Add("Access-Control-Allow-Origin", new [] {"http://cwfr003320:9393"});
            context.Response.Headers.Add("Access-Control-Allow-Credentials", new[] { "true" });
            context.Response.Headers.Add("Access-Control-Allow-Methods", new[] { "GET, POST, PUT, DELETE, OPTIONS" });
            context.Response.Headers.Add("Access-Control-Allow-Headers", new[] { "Accepts, Content-Type, Origin,Access-Control-Allow-Origin, Access-Control-Allow-Credentials" });
            context.Response.Headers.Add("Access-Control-Max-Age", new[] { "3600" });
            return; 
        }
        await _next.Invoke(context);
    }

But, i get a 401 code for the options request. How i can resolve this error ? With Anonymous authentication it's work correctly...

Thank you in advance.

Answer 1

You need to use IIS CORS module to allow preflight requests to go through Windows authentication,

https://blogs.iis.net/iisteam/getting-started-with-the-iis-cors-module