1. At an upstream service in a computerized environment in which the upstream service and one or more downstream services comprise a multi-tiered application system, a method of proving authority to communicate with the one or more downstream services, comprising the acts of: receiving an end-user request at an upstream service for one or more actions to be performed by a multi-tiered application system; determining that the end-user request involves an action to be performed by a downstream service; requesting one or more security tokens from a security token service, wherein the one or more security tokens identify the upstream service; creating a secure communication channel with the downstream service using at least one of the one or more security tokens, wherein the upstream service proves authority to communicate with the downstream service as a trusted subsystem; and sending the end-user request to the downstream service over the secure communication channel.