We're struggling with performance issues with a ASP.NET MVC site that is using Windows Authentication. Response time is very slow on the first request to the site when the user is being authenticated. Further, every time the Authorization header is sent from the browser the response time increases with many seconds. The same issue occurs for both executed files and static content like CSS and JS. Access to the application is restricted to users within a certain role and we are now planning to allow access to static files for all authenticated users to see if that helps. The authentication method in use is NTLM. How should we go forward in pinpointing why authentication decreases performance drastically?