OptionSAML_IDP_ENTITY_ID
Description IDP identifier used internally in the authentication flow

This identifies your IDP and is used internally in the authentication flow.

ini
...
SAML_IDP_ENTITY_ID=$IDP_ENTITY_ID
...

The value of $IDP_ENTITY_ID would be a URL, for example: https://accounts.google.com/o/saml2?idpid=C0453.