mod_http_oauth2: Fix returning errors from response handlers This would either redirect the user back to the client along with the error code, or show the error HTML template. Previously this would just show some JSON to the user.

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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.