According to an embodiment of the invention, a system for processing a plurality of service requests in a client-server system includes a challenge server for: presenting a cryptographic challenge to the client; initializing a trust cookie that encodes a client's initial priority level after the client correctly solves the cryptographic challenge; computing a trust level score for the client based on a service request wherein said trust level score is associated with an amount of resources expended by the server in handling the service request such that a higher trust level score is computed for service requests consuming less system resources; assigning the trust level score to the client based on the computation; and embedding the assigned trust level score in the trust cookie included in all responses sent from the server to the client. The system further includes an application server coupled with a firewall.