Selecting user in createUiDefinition (and getting the user object id)

Question

I'm creating a solution template (potentially azure managed application) which has a keyvault. I would like to add the access policy for the user who deploys the resource so that secrets can be viewed by the user creating the deployment without manually adding afterwards. However, I cannot see a way to get this from the createUiDefinition file. There is a UI controls for ServicePrincipalSelector and ManagedIdentitySelector but neither can select users. However, the Key Vault resource does provide support for this. Is it possible in the createUiDefinition? Alternatively, I would be happy to just access the objectId from the user if that were available somewhere in the ARM template (i.e. output from az ad signed-in-user show | jq .id)? Does anyone have any suggestions?

Thanks, Paul