When connecting to embedded devices that implicitly allow SSH access guacd fails when the authentication method is (none). The devices permit any SSH user with no password access to the console, and then provide authentication internally via their interactive shell.
- no username and no password configured: Guacamole requests both, then fails to connect.
- username but no password: Guacamole requests password, and then fails to connect.
- username and password: Guacamole asks for no input, and then fails to connect.
I've attached guacd debug logs from the failed connection attempts, plus OpenSSH (-vv) logs from a successful connection. (Files have been suitably redacted). The bit they share in common is they both state "Authentication (none)" but OpenSSH proceeds with the connection, while guacd terminates the connection: