Getting cert serial from an OCSP single response

[Geoff Swan]

I've been going over the openssl-3 documentation, trying to upgrade some 
1.0.2 code but I think I might have missed something somewhere.

I'm trying to get the cert serial number (or the ocsp_certid structure) 
from an OCSP single response, obtained from a basic respose such as:

single = OCSP_resp_get0(br, i);

Is there a simple way to get the cert serial from the single response in 
openssl-3?

Thanks,

Geoff.