In this paper we introduce the notion of gate automata for describing security policies. This new kind of automata aim at defining a model for the specification of both security and trust policies. The main novelty of our proposal is a unified framework for the integration of security enforcement and trust monitoring. Indeed, gate automata watch the execution of a target program, possibly modifying its behaviour, and produce a feedback for the trust management system. The level of trust changes the environment settings by dynamically activating/deactivating some of the defined gate automata.