As the basic application of PKI (Public Key Infrastructure) theories and technologies, electronic authentication services (thereinafter referred to as EAS) is defined as to provide authentic identities and identity verification services for participants involved in network-based activities. Due to its complexity of constructing PKI, most application systems including e-business platforms need to integrate EAS provided by a third party into their own business processes. Based on exploration on the requirements of EAS for e-business together with careful study and engineering practice in this area, this paper presents a complete solution of EAS based on PKI for enabling e-business. Architecture of EAS and its functionality components are brought forth and illustrated first. Then we brought forward a cross-domain trust model and method of managing different trust sources to achieve cross-domain trust and configurable trust-policy. To integrate EAS with e-business systems agilely, we put forward an agile integrating solution utilizing technologies such as Web service and remote scripting.