I was looking for a way to create an audit policy to check whether two resource tags exist, and flag which resources are non-compliant with this. In this post, I give you the final policy JSON and step you through the process of taking what you know, to apply it to something new:
https://techcommunity.microsoft.com/t5/itops-talk-blog/how-to-build-an-audit-azure-policy-with-multi...
-Sonia
