Sorry, but if you had read the README you would probably have noticed that it does not matter if you use Google Auth, LDAP, MySQL or anything else. Subjects are just string identifiers, so it works per definition with everything, including LDAP.
This is a good example for separation of concerns. LDAP is for authentication, ladon is for Authorization. Don't mix those.
Kerberos and OAuth are examples of authentication protocols. LDAP is not principally designed for authentication, it is a protocol for reading and modifying an hierarchical directory service (think phone book, DNS, etc.), but the "LDAP bind" operation has often been pressed into service for authn.
This is a good example for separation of concerns. LDAP is for authentication, ladon is for Authorization. Don't mix those.