A client system may be configured to request a single sign on authentication, in which an identity certificate is provided by the client system and stored by a server system. The stored certificate may be used to later authenticate a secure connection between the client system and the server system, after validating that the user represented by the certificate is a legitimate registered user of the server. The secure connection validated by the stored certificate may be, for example, a secure sockets layer/transport layer security (SSL/TLS) connection.