Hi!
I ended up with the same issue. If you have the openssl tools available, you can extract the thingname directly from the certificate. It’s embedded in the “subject”. You can try this something like this:
openssl x509 -in cert.crt -subject -noout
You should get an output similar to this:
subject=C = , ST = , L = , O = , OU = , CN = e74d3774-ceff-493c-b3f9-398d4e9d7585
Your thingname can be extracted from the CN field.