A model for authentication and authorization of users and applications that use network services. A client requests a ticket by providing credentials (user ID and password), e.g., over HTTP/SOAP/XML in the UDDI framework. An authentication adapter in a receiving server deserializes the request into a data structure that provides access to the security ID and password attributes, and passes these attributes to an ID management system to perform authentication. The credentials also determine the user's or application's privileges. The authentication adapter constructs a ticket object for the client incorporating the privileges and other information, e.g., the security ID and a date/time stamp. The ticket object is serialized, encrypted, encoded for transmission and inserted into an appropriately-formatted XML message and returned to the requesting client. The client attaches the authentication ticket to subsequent service requests that require authentication. To validate the ticket, the ticket object is reconstructed from the request data.