Add step on how to get DN for allowedSubjectPatterns

Signed-off-by: Mahesh Nyayadhish <[email protected]>

Author: maheshnyayadhish

modules/nw-mutual-tls-auth.adoc

@@ -61,3 +61,9 @@ $ oc edit IngressController default -n openshift-ingress-operator
       allowedSubjectPatterns:
       - "^/CN=example.com/ST=NC/C=US/O=Security/OU=OpenShift$"
 ----
+. Optional, get the Distinguished Name (DN) for `allowedSubjectPatterns` by entering the following command.
+[source,terminal]
+----
+$ openssl  x509 -in custom-cert.pem  -noout -subject
+subject= /CN=example.com/ST=NC/C=US/O=Security/OU=OpenShift
+----