Mutiple Federations are configured by adding several
<MetataProvider> elements to the configuration file as defined in DSAddMetadata.
The precise user experience is controlled via the "provideList" and "provideListOfLists" elements as described in DSUserInterface.
If the users are liable to know which federation their IdP belongs to then provideListOfLists should be set to "true" and provideList is "false". The user is then confronted with a table with two columns, the first column selects the federation and the second the IdP within the federation.
If the user is unlikely to be able to chose the federation then provideListOfLists should be set to "false" and provideList is "true". The user will be confronted with a single long list with all the IdPs in it.