Although in theory this could be backwards-incompatible, in practice
returning Authority from checkAudience is enough for the only extension
that extends CentralIdLookup, CentralAuth
Change-Id: I976dc854bf26b202347c3b47e956b85bbee156de
This normalizes handling of transformations on the boundaries between
preferences and generic form controls and removes the special case
where email-blacklist is passed around as an array internally, leaking
into the API.
As a result of this normalization, meta=userinfo no longer returns an
array of users, using the internal representation like action=options.
Bug: T198935
Change-Id: Iff63da0d215585cfcf083e7f7ec8ed45d5b77301
