/usr/share/doc/openvpn/examples/sample-scripts/ucn.pl is in openvpn 2.3.10-1ubuntu2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 | #!/usr/bin/perl -t
# OpenVPN --auth-user-pass-verify script.
# Only authenticate if username equals common_name.
# In OpenVPN config file:
# auth-user-pass-verify ./ucn.pl via-env
$username = $ENV{'username'};
$common_name = $ENV{'common_name'};
exit !(length($username) > 0 && length($common_name) > 0 && $username eq $common_name);
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