The REST security design principle of complete mediation requires that a system must validate access rights to all its resources for every request and must not rely on a cached permission matrix. This principle ensures that any changes in access rights are immediately enforced and that outdated permissions do not compromise security. References: REST Security Design Principles - Medium1; Design Principles - Clemson3.https://medium.com/strike-sh/rest-security-design-principles-434bd6ee57ea