Extension attribute to report on certificate expiration - https://jamfnation.jamfsoftware.com/discussion.html?id=3631

checkUser.pl

#!/usr/bin/perl -w
#
open(CERTS, "security export -k login.keychain -t certs|");
my $ifile = "";
my $thisfile = "";
$username = $ENV{USER};
print "Found user name: $username\n";
$dsclmodulus = `/usr/bin/dscl localhost read /Search/Users/$username UserCertificate |
                        /usr/bin/sed -e 's/UserCertificate://' |
                        /usr/bin/xxd -r -p | openssl x509 -inform DER -outform PEM |
                        /usr/bin/openssl x509 -noout -modulus` ;
while(<CERTS>) {
   $ifile .= $_;
   $thisfile .= $_;
   if($_ =~ /^\-+END(\s\w+)?\sCERTIFICATE\-+$/) {
      $subject = `echo "$thisfile" | /usr/bin/openssl x509 -noout -subject`;
      chomp($enddate = `echo "$thisfile" | /usr/bin/openssl x509 -noout -enddate`);
      $enddate =~ s/notAfter=//g;
        print "Checking Certificate: $subject";
        if($subject =~ m/$username/){
                $crtmodulus = `echo "$thisfile" | /usr/bin/openssl x509 -noout -modulus`;
                print "Checking Certificate: $crtmodulus";

                if($crtmodulus = $dsclmodulus){
                        print "Found Certificate Match\n: $subject";
                        print "<result>$enddate</result>\n";
                        exit 1;
                }
        }
      $thisfile = "";
        }
}
close(CERTS);
exit 0

Example Output
/Users/acid/Dropbox/certcheckuser

Found user name: acid
Checking Certificate: subject= /CN=Apple Configurator (00:00:00:00:00:D8)/O=sand.wallcity.org/C=US
Checking Certificate: subject= /DC=example/DC=org/DC=wallcity/CN=Users/CN=Zack Smith/emailAddress=acidprimePLEASEDONT@SPAMMEwallcity.org
Checking Certificate: Modulus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
Found Certificate Match
: subject= /DC=example/DC=org/DC=wallcity/CN=Users/CN=Zack Smith/emailAddress=acidprimePLEASEDONT@SPAMMEwallcity.org
Oct 3 21:53:59 2012 GMT<\result>