mod_http_oauth2: Create proper template for OOB code delivery This also improves security by reusing the security and cache headers, where mod_http_errors/http-message doesn't add such headers. Colors selected by taking rotating the error colors, rrggbb -> ggbbrr

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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.