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+#!/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;