IDP Selection and discovery helps your Service Provider determine which Identity Provider should be used for authentication of the current user. Access Manager supports IDP discovery through “Use Introductions”. When Introductions are configured, it allows users to select an identity provider from a list of introducible identity providers. https://www.netiq.com/documentation/access-manager-42/admin/data/b1ax6f15.html#bmpx02e In some cases this approach might not be viable, in those scenarios custom IDP discovery service might be useful.
When common domain and introductions are not viable User has to select authentication cards, but every time user has to select his IDP external authentication contract it is not a user friendly approach in some of the scenarios. Showing a list of IDPs and remember user selection might be a good and easy way to solve this issue.
NAM will present a list of available IDPs the user can select and save that selection to the client browser, next the user will not see this IDP selection page, the user will be redirected to his/her choice of IDP. The following solution is based on NAM 4.2 and above.