mod_http_oauth2: Separate extracting credentials from requests and verifying The token endpoint also uses Basic auth, but the password would be the client_secret, so we need to verify against that instead of using test_password(). Splitting this up here avoids code duplication. Possibly this new function could go into util.http...

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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.