Can't you do "*.hostname.com" asp.net mvc handles it for me and I have subdomains for each customer and they log in and operate in their subdomain. All special

Can't you do "*.hostname.com" asp.net mvc handles it for me and I have subdomains for each customer and they log in and operate in their subdomain. All special cookie flags are configurable so it keeps top security. Getting cookies across domains is something you don't want to do, so I have kind of idea that maybe, probably you are doing something wrong. My advice is "use proper framework".