[keycloak-user] Mapping a user attribute to a custom claim

Hi all, I've configured Google and Github as Identity Providers. I would like to have one of the user attributes, the email, mapped to a custom claim, called "userPrincipalName". I tried creating an Attribute Importer mapper, with Social Profile JSON Field Path = emailaddress User Attribute Name = userPrincipalName but this does not seem to work. Is there a way to log the JSON token obtained from the identity provider, so that I can have an idea of what should go in the " Social Profile JSON Field Path" field? Thanks, Paolo