Most likely your certificate isn't trusted by oxAuth.
To quickly confirm it's the cause, edit `/etc/gluu/conf/ox-ldap.properties` file by commenting next lines out, as shown below:
Then restart "oxauth" service. That will disable certificate verification.
As a more secure solution, consider adding your LDAP server's certificate (the server itself, not root CA's) to `/etc/certs/opendj.pkcs12` truststore.