Just for posterity since I thought I was going crazy:
If you get errors like
Unrecognized field: randomId
for your /oauth/v2/auth page, or perhaps
{"error":"redirect_uri_mismatch","error_description":"The redirect URI provided does not match registered URI(s)."}
when you get past that error, the problem is that FOSOAuthServerBundle needs to be in the Doctrine mappings so that base model attributes are added to the database. (Obviously any database migrations also need to be created or applied as well so this data can be persisted.)
config.yml:
doctrine:
orm:
entity_managers:
default:
mappings:
FOSOAuthServerBundle: ~
Once again, reading the instructions pays off :)