Check-Alexa-Timestamp-Tolerance names a function, with lambda list (BODY-JSON):
Ensure that the timestamp of an Alexa-sent query is within the allowed tolerance.
Excerpt from Amazon requirements at https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html:
Checking the Timestamp of the Request
Every request sent to your web service by Alexa includes a timestamp. This information is part of the signed portion of the request, so it cannot be changed without also invalidating the request signature. Using this timestamp to verify the freshness of the request before responding protects your service from attackers attempting a "replay" attack in which they acquire a properly signed request and then repeatedly resend it to disrupt your service.
Your service should allow a tolerance of no more than 150 seconds (two and a half minutes). This means that your service should only accept requests in which the request timestamp is within 150 seconds of the current time. Web services that allow a longer tolerance cannot be published to Amazon customers.
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If you are not using the Java library, you need to do this verification yourself. The timestamp is provided as part of the request object in the JSON body of the request … The timestamp is provided as an ISO 8601 formatted string (for example, 2015-05-13T12:34:56Z). Your code needs to parse the string into a date object, then verify that it is within the tolerance your web service allows (no more than 150 seconds). Reject requests in which the timestamp falls outside the tolerance with an error code (such as 400 Bad Request).
Defined in file src/endpoints/gossip/alexa/alexa.lisp.