— This paper proposes an authentication approach to support multi-clients in using a multi-application based environment. The approach is primarily based on the public key infrastructure (PKI) authentication scheme and the multi-agent technique. A key pair and a certificate issued by the Certification Authority (CA) are normally kept in a smart card or a token in order to enforce two-factor authentication. Both key pair and certificate are deployed to encrypt/decrypt electronic data or transaction, or sign/authenticate the sender and the recipient. We apply the Single Sign-On (SSO) and the Multi-Agent System (MAS) concepts to facilitate the authentication and the authorization process in order to work with multi-applications and multi-clients more dynamically and efficiently. The agent system functions when each client requests to sign on and it is responsible for validating a client certificate, granting an access role to the client, and controlling a concurrent use of applications....