Abstract: A security broker (SB) that provides network based authorization of secure VoIP services, triggered upon attempted user access. The security broker (SB) intercepts a SIP transaction during session setup to transmit a network based security challenge to a SIP application attempting to access (secure) IP based services. A network based security challenge is transmitted to a participating SIP application on both the origination and termination legs of a SIP transaction. The network based security challenge prompts a SIP application to return subscriber authorization/authentication credentials (e.g. a username/password combination). If credentials returned by the SIP application are valid, the security broker (SB) authorizes the network to permit session completion, and access to secure IP services is granted.