Reduce log level for unauthorized actions

Currently, every time an unauthorized participant contacts an endpoint we get alerted. This is definitely lower in severity, but we still probably want to know about this at some point. Figure out some better mechanism.

cc @yourbuddyconner

No files or tests are named. Locate the endpoint handling and logging for unauthorized participant requests, then determine how lower-severity events should remain available for later review; done requires an agreed mechanism that avoids alerting on every event while preserving visibility.

Written by the indexing model from the issue text.