Least privilege

Least privilege says access should match need: the minimum set of entitlements required for the work someone is actually doing, granted for no longer than the work lasts. It is the oldest principle in access control, and the most commonly violated, because granting broadly once is easier than granting precisely many times.

Why it decays without enforcement

Nobody sets out to over-provision. Access accumulates through defensible one-off decisions (a project, an incident, a role change where the old access never left), and the sum is privilege creep. Least privilege is therefore not a setup task but a maintenance loop: policies that state what each population should hold, reviews that catch the drift, and expiry (just-in-time access) that prevents the standing grants from forming at all.

Making it checkable

The principle only bites when it is written down as something a machine can evaluate. "Engineers should have repo access" is a sentiment; "the Engineering segment holds these entitlements, and holding more is a finding" is a control. Ploy's policies take the second form, so least privilege becomes a measurable state rather than a value statement.