To login you need to provide the unhashed value of "updater.secret" in your config file.

If you don't know that value, you can access this updater directly via the Nextcloud admin screen or generate your own secret:

php -r '$password = trim(shell_exec("openssl rand -base64 48"));if(strlen($password) === 64) {$hash = password_hash($password, PASSWORD_DEFAULT) . "\n"; echo "Insert as \"updater.secret\": ".$hash; echo "The plaintext value is: ".$password."\n";}else{echo "Could not execute OpenSSL.\n";};'