This method works by sending a signature created with a private key of the user. The server MUST check that the key is a valid authenticator for the user, and MUST check that the signature is valid. If both hold, the authentication request MUST be accepted; otherwise, it MUST be rejected.
string session identifier byte SSH_MSG_USERAUTH_REQUEST string user name string service name string "publickey" boolean TRUE string public key algorithm name string public key to be used for authentication