It's sad how smart they tried to be when adding the backdoor: "the corresponding
password for this username is derived by concatenating the PBX's serial number,
the string 'r2d2,' and the current date [in the format 'http://DD.MM.YYYY'],
..."
https://thehackernews.com/2021/12/secret-backdoors-found-in-german-made.html?m=1