A dynamic authorization callback mechanism is provided that implements a dynamic authorization model. An application can thus implement virtually any authorization policy by utilizing dynamic data and flexible policy algorithms inherent in the dynamic authorization model. Dynamic data, such as client operation parameter values, client attributes stored in a time-varying or updateable data store, run-time or environmental factors such as time-of-day, and any other static or dynamic data that is managed or retrievable by the application may be evaluated in connection with access control decisions. Hence, applications may define and implement business rules that can be expressed in terms of run-time operations and dynamic data. An application thus has substantial flexibility in defining and implementing custom authorization policy, and at the same time provides standard definitions for such dynamic data and policy.