mod_http_oauth2: Record hash of client_id to allow future verification RFC 6819 section 5.2.2.2 states that refresh tokens MUST be bound to the client. In order to do that, we must record something that can definitely tie the client to the grant. Since the full client_id is so large (why we have this client_subset function), a hash is stored instead.

This module helps reduces power usage of inactive mobile clients while
another client is actively used. E.g. in the case of chatting on a
desktop computer, instantly pushing messages to a phone in someones
pocket is not the best use of radio time.

Works with [mod_csi_simple][doc:modules:mod_csi_simple] which is
included with Prosody since 0.11