OPC UA certificates infrastructure for the connector for OPC UA

The connector for OPC UA is an OPC UA client application that lets you connect securely to OPC UA servers. In OPC UA, the security includes:

• Application authentication
• Message signing
• Data encryption
• User authentication and authorization.

This article focuses on application authentication and how to configure the connector for OPC UA to connect securely to your OPC UA servers at the edge. In OPC UA, every application instance has an X.509 certificate that it uses to establish trust with the other OPC UA applications it communicates with.

To learn more about OPC UA application security, see Application Authentication.

Connector for OPC UA application instance certificate

The connector for OPC UA is an OPC UA client application. The connector for OPC UA makes use of a single OPC UA application instance certificate for all the sessions it establishes to collect telemetry data from OPC UA servers. A default deployment of the connector for OPC UA uses cert-manager to manage its application instance certificate:

• Cert-manager generates a self-signed OPC UA compatible certificate and stores it as Kubernetes native secret. The default name for this certificate is aio-opc-opcuabroker-default-application-cert.
• The connector for OPC UA maps and uses this certificate for all the pods it uses to connect to OPC UA servers.
• Cert-manager automatically renews certificates before they expire.

By default, the connector for OPC UA connects to an OPC UA server by using the endpoint with the highest supported level of security. Therefore, a mutual trust handshake between the two OPC UA applications must be established beforehand. To enable mutual application authentication trust, you need to:

• Export the public key of the connector for OPC UA application instance certificate from the Kubernetes secret store and then add it to trusted certificates list for the OPC UA server.
• Export the public key of the OPC UA server's application instance and then add it to trusted certificates list for the connector for OPC UA.

Mutual trust validation between the OPC UA server and the connector for OPC UA is now possible. You can now configure an AssetEndpointProfile for the OPC UA server in the operations experience web UI and start working with it.

The connector for OPC UA trusted certificates list

You need to maintain a trusted certificate list that contains the certificates of all the OPC UA servers that the connector for OPC UA trusts. To create a session with an OPC UA server:

• The connector for OPC UA sends its certificate's public key.
• The OPC UA server validates against its trusted certificates list.
• A similar validation of the OPC UA server's certificate happens in the connector for OPC UA.

By default, the connector for OPC UA stores its trusted certificate list in Azure Key Vault and uses the Secrets Store CSI Driver to project the trusted certificates into the connector for OPC UA pods. Azure Key Vault stores the certificates encoded in DER or PEM format.

If the connector for OPC UA trusts a certificate authority, it automatically trusts any server that has a valid application instance certificate signed by the certificate authority.

To project the trusted certificates from Azure Key Vault into the Kubernetes cluster, you must configure a SecretProviderClass custom resource. This custom resource contains a list of all the secret references associated with the trusted certificates. The connector for OPC UA uses the custom resource to map the trusted certificates into connector for OPC UA containers and make them available for validation. The default name for the SecretProviderClass custom resource that handles the trusted certificates list is aio-opc-ua-broker-trust-list.

The connector for OPC UA issuer certificates list

If your OPC UA server's application instance certificate is signed by an intermediate certificate authority, but you don't want to automatically trust all the certificates issued by the certificate authority, you can use an issuer certificate list to manage the trust relationship.

An issuer certificate list stores the certificate authority certificates that the connector for OPC UA trusts. If the application certificate of an OPC UA server is signed by an intermediate certificate authority, the connector for OPC UA validates the full chain of certificate authorities up to the root. The issuer certificate list should contain the certificates of all the certificate authorities in the chain to ensure that the connector for OPC UA can validate the OPC UA servers.

You manage the issuer certificate list in the same way you manage the trusted certificates list. The default name for the SecretProviderClass custom resource that handles the issuer certificates list is aio-opc-ua-broker-issuer-list.

Features supported

The following table shows the feature support level for authentication in the current version of the connector for OPC UA: