mod_http_oauth2: Calculate client secret expiry in registration response Not actually the client_secret that expires, but the client_id JWT. Returning '0' indicating no expiry was incorrect unless JWT expiry is turned off, which we check for now.

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summary: Log a message once per minute
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This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.