Can I connect Microsoft Sharepoint to an IdP?

Yes, but the setup is not trivial and may not be suited your environment. ISC’s WebLogin team offers no application-specific support for Sharepoint, but Microsoft has created a Step-by-Step Guide: Federated Collaboration with Shibboleth 2.0 and SharePoint 2010 technologies for those interested in performing such an integration. The solution offered in the above document allows an IdP user to access Sharepoint both as a web application and also directly through Microsoft Office 2010 applications. Before attempting a project like this, know that it has the potential be to very complex.