You could also use LDAP as in interface for user management. This is a tighter bundling that requires the ports be opened, an account be created in LDAP with appropriate permissions, knowledge of the LDAP schema and LDAP DIT... but there is nothing you can't do in LDAP, while SCIM still has some limitations. For simple ADD / DELETE user, SCIM is fine.
SCIM is just JSON / REST. A SCIM client library just makes it easier for a programmer to handle the security requirements and exact protocol.