HTTP Post does not redirect to next page

Hi,
I have created login for site. I am using "UserLogin.ascx" which is placed in masterpage. Now I have to create the Login system so that the users from other sites login to my site through Http post or Get. I have created the page for sending "HTTP Post" to my site and it also login to my site, but when I click on any link it logs out also in the browser's address bar the URL of the previous site is shown.

Thanks
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