Open Policy Agent (OPA) is an open source, general-purpose policy engine. Open Policy Agent is used to evaluate policies against structured data to make sure that the data passes the policy checks. OPA evaluates policies specified in Abbey Grant Kits and resolve as true or false when an Access Request is made. Abbey creates a structured data payload based on attributes and other information about a user, which is used as input to Policy Evaluation. On a false evaluation, the policy check fails, and the Access Request is denied.