int libssh2_userauth_publickey_fromfile_ex(LIBSSH2_SESSION *session, const char *username, unsigned int ousername_len, const char *publickey, const char *privatekey, const char *passphrase);
username - Pointer to user name to authenticate as.
username_len - Length of username.
publickey - Path name of the public key file. (e.g. /etc/ssh/hostkey.pub). If libssh2 is built against OpenSSL, this option can be set to NULL.
privatekey - Path name of the private key file. (e.g. /etc/ssh/hostkey)
passphrase - Passphrase to use when decoding privatekey.
Attempt public key authentication using a PEM encoded private key file stored on disk
LIBSSH2_ERROR_SOCKET_SEND - Unable to send data on socket.
LIBSSH2_ERROR_SOCKET_TIMEOUT -
LIBSSH2_ERROR_PUBLICKEY_UNVERIFIED - The username/public key combination was invalid.
LIBSSH2_ERROR_AUTHENTICATION_FAILED - Authentication using the supplied public key was not accepted.