How can I install and use a custom JDBC connection in Looker? From conversations with the Looker team, I know this wouldn’t be supported and could be broken by future Looker changes, but we would take responsibility to test the custom JDBC connection...

We have a requirement to call an external API to determine whether a user has permission to perform a given action. The use case is for Looker to call this external API with the current username and tables/view before proceeding with the query.