Grafana's default installation of `synthetic-monitoring-agent` exposes sensitive information

Summary

The Synthetic Monitoring Agent for Grafana's Synthetic Monitoring application provides probe functionality and executes network checks for monitoring remote targets. Users running the Synthetic Monitoring agent prior to version 0.12.0 in their local network are impacted. The authentication token used to communicate with the Synthetic Monitoring API is exposed through a debugging endpoint. This token can be used to retrieve the Synthetic Monitoring checks created by the user and assigned to the agent identified with that token. The Synthetic Monitoring API will reject connections from already-connected agents, so access to the token does not guarantee access to the checks. Version 0.12.0 contains a fix. Users are advised to rotate the agent tokens. After upgrading to version v0.12.0 or later, it's recommended that users of distribution packages review the configuration stored in `/etc/synthetic-monitoring/synthetic-monitoring-agent.conf`, specifically the `API_TOKEN` variable which has been renamed to `SM_AGENT_API_TOKEN`. As a workaround for previous versions, it's recommended that users review the agent settings and set the HTTP listening address in a manner that limits the exposure, for example, localhost or a non-routed network, by using the command line parameter `-listen-address`, e.g. `-listen-address localhost:4050`.