Here is an OPC UA gateway with which you can access your OPC UA values via MQTT and GraphQL (HTTP). If you have an OPC UA server in your PLC, or a SCADA system with an OPC UA server, you can query data from there via MQTT and GraphQL (HTTP). In addition, the gateway can also log value changes from OPC UA nodes in an InfluxDB. The archived values can then also be queried via GraphQL.
In the TIA Portal you have to enable “Operate as OPC Server” in the Runtime Settings of your project. Download and restart the runtime, and then the OPC UA Server is listening on opc.tcp://localhost:4890.
You need to have a user which has a role with the OPC-UA read and write access permission.
When you try to connect with a client the client will send the certificate to the server and typically the certificate is rejected by the server. To trust the certificate you have to move the certificate from the “Rejected” folder to the “Trusted” folder.
Add a label object into your screen and add some lines of code to get a QR image. In this example a mobile phone app will scan the QR code and send username and password via a GraphQL server to WinCC OA and set it on datapoints (username and password should additionally be encrypted).