Constructor.
Existing certificate, typically issued by another CA.
Private key corresponding to cert
. This is preferably a low-level signer, but can also
accept a high-level signer that unconditionally signs the input regardless of packet name.
Create a message to continue the challenge.
Parameter key-value pairs to send to server in continuing CHALLENGE request.
Create a message to select and start the challenge.
Parameter key-value pairs to send to server in initial CHALLENGE request.
The "possession" challenge where client must present an existing certificate.