title: Azure policy to require a certain Tag be created, but not with a default value?
body: <p>Is there a way to create an Azure policy that requires a Tag exist on a resource when it's created, but not check for a specific value? All the examples I've seen are for "check if tag X is there, and has value Y". </p>
  
  <p>I want to simply let the user know "you need to put tag X on this resource" because the value is user-defined so I can't enforce a specific value.</p>
  
  <p>For example - I need "BillingCode" on every resource, but only the person creating the resource knows their correct billing code since it's different for each person or project.</p>