I'm sure you've heard the common phrase "a canary in a coal mine" when people talk about safety and detection of issues. When miners used to go down to work, there was a danger of trapped gasses being released as they were digging. Some of these gasses were hard for humans to detect and, if enough was breathed in, could lead to illness or even death. In order to help the miners detect and avoid these kinds of issues, they would take a canary (the bird) down into the mine with them.
[...] The idea of a "canary" value in the security world is pretty similar. A "canary" value is one that - real or faked - is somehow exposed outside of your own system. If this value is used you need to be notified immediately so you can take action and gather more information about the usage and any other associated issues.
The tutorial then introduces the psecio/canary package and shows some of its basic use detecting input and setting up notifications. It also covers some of the package's integrations for notifications with services like Slack, PagerDuty and custom Monolog handling. It also provides an example of it in a more "real world" situation of a Slim framework middleware that detects incoming