A credential store in memory, for tests and development.
Whether records survive the app quitting. Receiving credentials needs a durable store unless the configuration is for development: it also keeps an authorization in progress while the holder is at the issuer's pages.
Deletes the record; deleting one that doesn't exist isn't an error.
Stores record under id, replacing any record with that ID.
The record stored under id, or null.
Every record.