The Salesforce Community Cloud should support OpenId Connect Authentication Provider and Registration Handler, and SAML SSO and just-in-time provisioning for self-registration and SSO. OpenId Connect is a protocol that allows users to authenticate with an external identity provider and access Salesforce resources. A registration handler is a class that implements the Auth.RegistrationHandler interface and defines how to create new users or update existing users in Salesforce from the information received from the identity provider. SAML SSO is a protocol that allows users to log in to Salesforce with a single credential from an identity provider. Just-in-time provisioning is a featurethat allows creating or updating user accounts in Salesforce based on SAML assertions.

References: [OpenID Connect Authentication Providers], [Registration Handler Interface], [SAML Single Sign-On for Communities].