You need to build a discovery applications that can perform the lookup based on email, and then send the user to the Gluu Server authorization endpoint with the correct parameters in the request (to give the hint about which IDP). This topic is out of scope of community support. We do have some [partners](https://gluu.org/service-partners/) that could help you. Also, if you were to use [Gluu Solo](https://gluu.org/solo), then you could tap into the hourly support.