Hi, this should be relevant - https://docs.fortinet.com/document/forticloud/22.4.0/identity-access-management-iam/239279/external-...
External IdP roles allow external users to log in to a cloud portal using their company’s user credentials with a third-party ID provider. External IdP users are authenticated by their company's ID provider.
But also note this part: "IdP roles is a limited beta feature. New enrollment requests are not available at this time.". Your best bet will be to reach out to your Fortinet SE and ask them about the current status of the beta.
[ corrections always welcome ]