A Centralized Authentication & Authorization (CAA) system that facilitates secure communication between service clients and service providers. CAA comprises a Service Request Filter (SRF), a Service Client Authentication Program (SCAP), a Service Authorization Program (SAP), and an Authorization Database (ADB). The SRF intercepts service requests, extracts the service client's identifier from a digital certificate attached to the request, and stores the identifier in memory accessible to service providers. In the preferred embodiment, the SRF forwards the service request to a web service manager. The web service manager invokes SCAP. SCAP matches the identifier with a record stored in ADB. SAP queries ADB to determine if the service request is valid for the service client. If the service request is valid, SAP authorizes the service request and the appropriate service provider processes the service request.