RequireHttpsAttribute.cs

public class RequireHttpsAttribute : AuthorizationFilterAttribute
{
    public override void OnAuthorization(HttpActionContext actionContext)
    {
        if (actionContext.Request.RequestUri.Scheme != Uri.UriSchemeHttps)
        {
            actionContext.Response = new HttpResponseMessage(System.Net.HttpStatusCode.Forbidden)
            {
                ReasonPhrase = "HTTPS Required"
            };
        }
        else
        {
            base.OnAuthorization(actionContext);
        }
    }
}