We have a Web Application that uses Client Object Model to present data from SharePoint.
The Web Application is using a 3rd party SSO that uses ASP.NET Forms Authentication. The SSO is required by our customer to make it easy for their users to switch between their Web Applications.
The problem is, that we can't get this 3rd party SSO to work with SharePoint. If we configure our SharePoint Web Application to use the SSO the authentication works for files that doesn't depend on SharePoint e.g. helloworld.aspx which we have placed in application root. If we try to access SitePages/Home.aspx we get 403 FORBIDDDEN.
This is probably because the FedAuth cookie isn't set.
So we thought, that maybe the SSO could authenticate the user against SharePoint Web Application by setting the FedAuth cookie through the Client Object Model API. Is that possible and will setting this FedAuth cookie mean that the user afterwards can access any page in the SharePoint Web Application? (Any page that the user is granted access to of course)
Or how else can we get SSO to authenticate the user against the SharePoint Web Application as the user was logged in through Forms Authentication _forms/default.aspx?ReturnUrl=%2f_layouts%2fAuthenticate.aspx%3fSource%3d%252F&Source=%2F