I have been asked a lot lately how other STS providers could be used to federate authentication with Office 365 instead of using ADFS.
- Here is the listing of third-party STS services that have officially tested with Microsoft - http://technet.microsoft.com/en-us/library/jj679342.aspx.
- For information about Shibboleth Identity Provider with Office 365, please read here - http://technet.microsoft.com/en-us/library/jj205456.aspx. Here is another good whitepaper on AD FS 2.0 Federation with Shibboleth 2 and the InCommon Federation - http://technet.microsoft.com/en-us/library/jj205456.aspx.
Additionally there was an announcement about a new program to get third-party identity providers (STS providers) tested and approved with Office 365 quicker. If you want to get one that you are working approved, recommend to them to read this - http://blogs.office.com/2014/01/30/the-works-with-office-365-identity-program-now-streamlined/.