diff --git a/docs/user/openstack/invalid-https-certificates.md b/docs/user/openstack/invalid-https-certificates.md
new file mode 100644
index 00000000000..ee97aafbfbe
--- /dev/null
+++ b/docs/user/openstack/invalid-https-certificates.md
@@ -0,0 +1,92 @@
+# OpenShift 4.10 refuses legacy HTTPS certificates
+
+With OpenShift v4.10, HTTPS certificates not using the `Subject Alternative Names` fields will be rejected. Upgrades will be blocked if such certificates are detected in some areas; however OpenShift will not automatically check the underlying OpenStack infrastructure prior to upgrading or installing. This is what the following instructions will walk you through doing.
+
+This script checks and reports on all HTTPS endpoints in an OpenStack catalog. Populate the environment with OpenStack credentials for the target cloud, then run the following Bash script.
+
+Requirements:
+* Bash 4+
+* grep
+* [Python OpenStack client][openstack-cli]
+* [jq][jq]
+* [openssl 1.1.1l+][openssl]
+
+```bash
+#!/usr/bin/env bash
+
+set -Eeuo pipefail
+
+declare san
+san="$(mktemp)"
+readonly san
+
+declare invalid=0
+
+openstack catalog list --format json --column Name --column Endpoints \
+	| jq -r '.[] | .Name as $name | .Endpoints[] | [$name, .interface, .url] | join(" ")' \
+	| sort \
+	| while read -r name interface url
+do
+	# Ignore HTTP
+	if [[ ${url#"http://"} != "$url" ]]; then
+		continue
+	fi
+
+	# Remove the schema from the URL
+	noschema=${url#"https://"}
+	
+	# If the schema was not HTTPS, error
+	if [[ noschema == "$url" ]]; then
+		echo "ERROR (unknown schema): $name $interface $url"
+		exit 2
+	fi
+
+	# Remove the path and only keep host and port
+	noschema="${noschema%%/*}"
+	host="${noschema%%:*}"
+	port="${noschema##*:}"
+
+	# Add the port if was implicit
+	if [[ "$port" == "$host" ]]; then
+		port='443'
+	fi
+
+	# Get the SAN fields
+	openssl s_client -showcerts -servername "$host" -connect "$host:$port" </dev/null 2>/dev/null \
+		| openssl x509 -noout -ext subjectAltName \
+		> "$san"
+
+	# openssl returns the empty string if no SAN is found.
+	# If a SAN is found, openssl is expected to return something like:
+	#
+	#    X509v3 Subject Alternative Name:
+	#        DNS:standalone, DNS:osp1, IP Address:192.168.2.1, IP Address:10.254.1.2
+	if [[ "$(grep -c "Subject Alternative Name" "$san" || true)" -gt 0 ]]; then
+		echo "PASS: $name $interface $url"
+	else
+		i=$((i+1))
+		echo "INVALID: $name $interface $url"
+	fi
+done
+
+# clean the tmp files
+rm "$san"
+
+if [[ $invalid -gt 0 ]]; then
+	echo "${invalid} legacy certificates were detected. Update your certificates to include a SAN field."
+	exit 1
+else
+	echo "All certificates for this cloud are valid."
+fi
+```
+
+In case the script reports INVALID certificates, they will have to be replaced with formally valid certificates (containing SAN fields for the server) before installing or upgrading to OpenShift v4.10.
+
+## Legacy certificates
+
+The [OpenShift v4.6 release notes][4.6-release-notes] warned about the deprecation in OpenShift of HTTPS certificates exposing the protected names in the CommonName field. With v4.10, this deprecation is enforced in the clusters. HTTPS certificates must now use the `Subject Alternative Names` fields or be rejected.
+
+[openstack-cli]: https://docs.openstack.org/python-openstackclient/latest/ "OpenStackClient (aka OSC) is a command-line client for OpenStack that brings the command set for Compute, Identity, Image, Object Storage and Block Storage APIs together in a single shell with a uniform command structure"
+[jq]: https://stedolan.github.io/jq/ "jq is a lightweight and flexible command-line JSON processor."
+[openssl]: https://www.openssl.org/ "Cryptography and SSL/TLS Toolkit "
+[4.6-release-notes]: https://docs.openshift.com/container-platform/4.6/release_notes/ocp-4-6-release-notes.html#ocp-4-6-tls-common-name "OpenShift Container Platform 4.6 release notes"
diff --git a/docs/user/openstack/known-issues.md b/docs/user/openstack/known-issues.md
index 32c54c598a3..34424b1907a 100644
--- a/docs/user/openstack/known-issues.md
+++ b/docs/user/openstack/known-issues.md
@@ -2,6 +2,14 @@
 
 We have been tracking a few issues and FAQs from our users, and are documenting them here along with the known workarounds and solutions. For issues that still have open bugs, we have attached the links to where the engineering team is tracking their progress. As changes occur, we will update both this document and the issue trackers with the latest information.
 
+## HTTPS CommonName deprecation
+
+With OpenShift v4.10, HTTPS certificates must include the names for the server in the `Subject Alternative Names` field. Legacy certificates will be rejected with the following error message:
+
+> x509: certificate relies on legacy Common Name field, use SANs instead
+
+In order to validate your OpenStack infrastructure prior to installation or upgrade to v4.10, please refer to the [dedicated instructions](invalid-https-certificates.md).
+
 ## Resources With Duplicate Names
 
 Since the installer requires the *Name* of your external network and Red Hat Core OS image, if you have other networks or images with the same name, it will choose one randomly from the set. This is not a reliable way to run the installer. We highly recommend that you resolve this with your cluster administrator by creating unique names for your resources in openstack.