subdomain CORS in webApi 2 - asp.net

Question

I am using WebApi like I've learnt from http://t.co/mt9wIL8gLA
It all works well if I know exactly the perfect origin URI of my client's requests.
Too bad I am writing an enterprise-wide API, so my request to, say
http://apps.contoso.com/myApp/api/foobar
may come from apps all over my domain, say:
http://apps.contoso.com/CRMApp
http://apps.contoso.com/XYZ
http://www.contoso.com/LegacyApp
http://test.contoso.com/newApps/WowApp
...
and all the new apps my enterprise builds.
What is the best way to approach this? using Origins="*" is cheesy, adding origins to my WS source and redeploy is cheesier.
My current solution is writing a custom CorsPolicyAttribute like in http://www.asp.net/web-api/overview/security/enabling-cross-origin-requests-in-web-api#cors-policy-providers
and read the allowed origins from appsettings in web.config.
A LITTLE better could be, inside the custom attribute, checking if the request Origin: header is from contoso.com, maybe with a regexp, and add it to allowed origins.
I am wondering if there is a better, more standard, way.

Answer 1

Use a DynamicPolicyProviderFactory. That's what I use...I even posted a question about it the other day that kind of shows how to add the allowed domains to the web.config file.

Answer 2

I ended up just writing an AuthorizationFilterAttribute, although I might have just done a regular FilterAttribute.
public class FilterReferals : AuthorizationFilterAttribute
{
public override void OnAuthorization(HttpActionContext actionContext)
{
var request = actionContext.Request;
if (!AllowedReferers.GetAllowedReferersList().Contains(request.Headers.Referrer?.Host.ToLower()))
{
Challenge(actionContext);
return;
}
base.OnAuthorization(actionContext);
}
void Challenge(HttpActionContext actionContext)
{
var host = actionContext.Request.RequestUri.DnsSafeHost;
actionContext.Response = actionContext.Request.CreateResponse(HttpStatusCode.Unauthorized);
actionContext.Response.Headers.Add("WWW-Authenticate", string.Format("Basic realm=\"{0}\"", host));
}
}