Security is a critical component of grid systems and while there are numerous software components and tools that provide some capabilities relating to security, there are few complete end-to-end security systems that work for emerging grid infrastructures "out-of-the-box". Hence significant time and effort are needed for software evaluation, testing and integration of different software components despite the fact that most grid infrastructures have very similar requirements and needs. In this paper, we present GAMA, a GSI-based security infrastructure that is easy to deploy and supports multiple applications. GAMA consists of two component groups: a backend server component that creates and manages X.509 user credentials on behalf of the user, and a set of portal components that provide interfaces for both users and administrators. The GAMA server provides synchronization capability between portals and clusters, supports any SOAP-based rich clients, and supports legacy applications that rely on MyProxy.