Enterprise networks may host multiple services, located in (potentially physically distinct) servers; an example would be Web server farms using Web 2.0 and/or SOA-based technologies. A service is governed by a client service contract (CSC) that specifies, among other requirements, the rate at which the service may be accessed so that a particular service host is not unduly overwhelmed. We consider the case where the CSC limits the rate to a service provider to no more than X requests per second, with an observation/enforcement time interval of T seconds. In this paper we define, simulate, and analyze CASTS (credit-based algorithm for service traffic shaping), a service traffic shaping algorithm to meet the service access requirements (SAR) under the above constraints. Our analysis includes convergence times, responsiveness, and the verification whether the system respects the service contract.