In order to implement this efficiently, I have introduced the concept of
"singleton" backends -- currently, 'sys' and 'cubbyhole'. There isn't
much reason to allow sys to be mounted at multiple places, and there
isn't much reason you'd need multiple per-token storage areas. By
restricting it to just one, I can store that particular mount instead of
iterating through them in order to call the appropriate revoke function.
Additionally, because revocation on the backend needs to be triggered by
the token store, the token store's salt is kept in the router and
client tokens going to the cubbyhole backend are double-salted by the
router. This allows the token store to drive when revocation happens
using its salted tokens.
specify more concrete error cases to make their way back up the stack.
Over time there is probably a cleaner way of doing this, but that's
looking like a more massive rewrite and this solves some issues in
the meantime.
Use a CodedError to return a more concrete HTTP return code for
operations you want to do so. Returning a regular error leaves
the existing behavior in place.
