1. An authorization engine for enforcing a group-centric secure authorization policy, the authorization engine comprising: a processor accessible by a user and configured to execute instructions; a memory containing an access-limited object and further containing executable instructions configured to instruct the processor to execute a stateful security policy, including the operations: define a group; receive a join command wherein the user joins the group as a member; receive a leave command wherein the user leaves the group; receive an add command wherein the object is added to the group as to be in the group; receive a remove command wherein the object is removed from the group; and authorize the user to access the object only when the user is a member of the group and the object is in the group; wherein the stateful security policy is based on an authorization equivalent to a stateless security policy; wherein the stateful security policy is configured to enforce well-formedness constraints including: the object cannot both be added to the group and removed from the group within the same state; the user cannot both join the group and leave the group within the same state; two types of operations cannot both occur in the same state for the user or the object; after joining the group, the user cannot join again unless the user has left the group since joining the group; after being added to the group, the object cannot be added to the group again unless it has been removed from the group since joining the group; the user cannot leave the group when the user is not already a member of the group; and the object cannot be removed from the group unless the object is already in the group; and wherein the stateful security policy further sorts operations by time and provides an order of precedence wherein: when add and join occur in the same state, add follows join; when join and remove occur in the same state, join follows remove; when add and leave occur in the same state, add follows leave; and when remove and leave occur in the same state, there is no fixed precedence.