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.

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summary: Remote Roster Management
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Introduction
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This module adds support for [XEP-0321: Remote Roster Management] which
is commonly used to allow components such as transports to modify the
rosters of local users.