Function approved 

fn approved(grant: &Grant) -> ScopeSet

What a stored login was approved at. A string that will not parse grants nothing, which is the safe direction for a value this crate rendered with ScopeSet’s own Display.

The empty set authorizes nothing, so a grant that stops parsing — after a grammar change, say — is a login that has quietly gone inert. It says so, the way stored_client_id says so about the other half of the same stored row.