I was working on setting up Forms authentication with Active directory for external authentication web application and wanted to have a link for an internal user. This link when clicked inside corporate network, would authenticate automatically using windows credentials without requiring user (eg.employee) to enter their username/password. Refer to the following custom login screen.
We setup server certificates for SSL and forms authentication is working well. When it comes to the intenal link, I keep receiving the following error.
When user click this link, we redirect to _windows/default.aspx page which takes care of windows authentication. _windows is a virtual directory that is referred to the TEMPLATE\IdentityModel folder under SharePoint root.
I search much of google but could not find the cause of this error. Finally it turned out to be 'HTTPS'. The site I am working on is an external site and is configured for 'HTTPS'. As soon as I took out SSL, it worked.