For secured communication over https a TLS certificate (containing public and private key) has to be supplied. The certificate for the web server can be imported via the Hardware Compiler import-certificate command using the purpose WebServer. The certificate will be persisted encrypted in the SecurityConfiguration.json file under the hwc.gen folder of the given PLC.
apax hwc import-certificate -i ./my-hw-config.hwl.json -n PLC_1 --purpose WebServer --certificate ./my-certificate.p12