Today, there are various cloud computing services. With only a few clicks, users can get the ondemand resources and services over internet without regard to where the services are hosted or how they are delivered. Moreover, the computing will become a kind of services that similar to traditional utilities such as water, gas, electricity, and telephony in the near-future. However, there are some security issue in Cloud computing should be solved. In this paper, we propose authentication-as-a-services (AaaS) architecture to provide a trust authentication infrastructure. In this design, user’s sensitive information will not leak to the service provider. Moreover, user can roaming in various service providers without re-registration and reauthenticate. This design is a foundation for meshing-up a trust and anonymous Cloud computing.