通过WIF在ADFS中进行用户名/密码验证

I'm building a REST web service mobile apps authentication - take username and password, authenticate in ADFS (preferably through WIF if possible) and returns the SAML (2.0) token back to caller. It's used for authorization in later calls. I found many guides and blog posts about authentication through WIF in web apps and authorization in WCF when the token is passed in call but I haven't found any clue how to approach this scenario. Any suggestions how to start?I'm building a REST web service mobile apps aut