This feature was added in VuFind 8.0.

Typical usage of Shibboleth authentication in a multi ILS environment is as follows:

You configure Shibboleth as an alternative authentication method and library cards are connected to that account using ILS username and password (through ILS driver)

But in the case where you want to connect your VuFind instance to multiple Shibboleth identity providers and also enable connecting accounts through library cards, you have to set it explicitly.

1. Set Shibboleth to point out to WAYF/DS instead of a single identity provider. See more about identity provider discovery here: Shibboleth.net - Identity Provider Discovery.
2. Enable option allow_configuration_override in the [Shibboleth] section of config.ini.
3. In the Shibboleth.ini configuration file, map the entityId of needed identity providers to instance names corresponding with multi-backend configuration in MultiBackend.ini and eventually overwrite default attributes mapping for particular identity providers.

The configuration option for this feature is in the [Catalog] section of config.ini and is called auth_based_library_cards. Just uncomment the example - set it to true.