Hi Michael,
There are 2 ways to solve this issue
1. You can set `trust_all_certs` field to `true` in oxd-server.yml. Then restart oxd and test register-site. In this case, oxd will trust all certificates.
2. Or you can import Open ID provider (i.e. Gluu server) certificate in oxd trust-store (i.e oxd-server.keystore file). If the certificate or Certificate Authorities presented by the external OP server is not in our oxd truststore, we'll get an SSLHandshakeException and the connection won't be set up successfully.
For #2 you may take reference of below link where `let's encrypt` ssl certificate was first added to Gluu server and then was add in truststore of oxd client.
https://www.gluu.org/docs/oxd/install/#configuring-lets-encrypt-ca-trusted-certificates-in-gluu-ce-server-and-oxd
Regards
Arnab