Methods, apparati, and computer-readable media for providing authorization and other services. In a preferred embodiment, an authorization service includes both a messaging specification and a set of rules that govern its use. A first customer wishing to use the authorization service prepares a request that complies with the service's messaging specification and transmits it to a first participant. The first participant transmits the request to a second participant, which processes the request according to authorization information provided by a second customer and rules that have been specified for the service. The second participant then prepares a response that complies with the service's messaging specification.