Information about type of authorization in Access to Control Panel:

Password authentication is available to users who have selected the option at registration "by password" it means that the registration process was used CSR (Generating a certificate request) type of BASIC in which personal certificate was generated by the server and is assigned to the user PKPID.

Authorization by certificate in Control Panel implemented based on standard X.509 which written in RFC number 1422 and published "Internet Engineering Task Force(IETF)" which is organizational unit of "Internet Society(ISOC)", full name document is RFC 1422.