如何使用ASP.NET和iframe对跨域的用户进行身份验证？

I am doing an ASP.NET website for a client, who wants to make their reports page available via IFRAME on other "reseller" websites. The reseller websites are providing the same service with different branding. I need to avoid, where I can, requiring them to implement any code on their webserver to enable this - hence using iframes.I am doing an ASP.NET website for a client, who