#!/usr/bin/perl
 
 # verify-cn -- a sample OpenVPN tls-verify script
 #
 # Return 0 if cn matches the common name component of
 # X509_NAME_oneline, 1 otherwise.
 #
 # For example in OpenVPN, you could use the directive:
 #
 #   tls-verify "./verify-cn Test-Client"
 #
 # This would cause the connection to be dropped unless
 # the client common name is "Test-Client"
 
 die "usage: verify-cn cn certificate_depth X509_NAME_oneline" if (@ARGV != 3);
 
 # Parse out arguments:
 #   cn    -- The common name which the client is required to have,
 #            taken from the argument to the tls-verify directive
 #            in the OpenVPN config file.
 #   depth -- The current certificate chain depth.  In a typical
 #            bi-level chain, the root certificate will be at level
 #            1 and the client certificate will be at level 0.
 #            This script will be called separately for each level.
 #   x509  -- the X509 subject string as extracted by OpenVPN from
 #            the client's provided certificate.
 ($cn, $depth, $x509) = @ARGV;
 
 if ($depth == 0) {
     # If depth is zero, we know that this is the final
     # certificate in the chain (i.e. the client certificate),
     # and the one we are interested in examining.
     # If so, parse out the common name substring in
     # the X509 subject string.
 
     if ($x509 =~ /\/CN=([^\/]+)/) {
 	# Accept the connection if the X509 common name
 	# string matches the passed cn argument.
 	if ($cn eq $1) {
 	    exit 0;
 	}
     }
 
     # Authentication failed -- Either we could not parse
     # the X509 subject string, or the common name in the
     # subject string didn't match the passed cn argument.
     exit 1;
 }
 
 # If depth is nonzero, tell OpenVPN to continue processing
 # the certificate chain.
 exit 0;