To address the scalability and identity federation problems of the traditional single sign-on system, the proposed scheme divides the security systems into different security domains. Each security domain has its own security servers and service providers, and there are trust relationships between different security domains for identity federation. The security server is responsible for authentication and authorization inside the domain, and offers identity federation capability for different domains. The security assertion markup language （SAML） assertion is used as security token in the system for authentication, authorization, and identity federation. The design of the proposed single sign-on process is based on web service security framework and multiple security domains, and the authorization is always deployed in the local area inside the service provider＇ s security domain, which enables web service clients, both inside and outside their security domains, to access the services in a simple, scalable, standard and secure way.
