In accordance with an embodiment, described is a system and method for integrating a transactional middleware platform with a centralized access manager to provide single sign-on authentication in an enterprise-level computing environment. The enterprise-level computing environment can include the transactional middleware platform and one or more SOA middleware platforms. Each middleware platform can include one or more access agents to access the centralized access manager configured to store user identity and security policy information for the enterprise-level computing environment. A request from a client for an application service in the transactional middleware platform can be intercepted by an access agent therein, which can communicate with a centralized access server of the centralized access manager to obtain a session token. The session token can be stored in an execution context of the client, for use in authorizing the client to access resources in each middleware platform in the enterprise-level computing environment.