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The relationship-focused and credential-focused identity managements are both user-centric notions in Service-oriented architecture (SOA). For composite services, pure user-centric identity management is inefficient because each subservice may authenticate and authorize users and users need participate in every identity provisioning transaction. If the above two paradigms are unified into the universal identity management where identity information and privileges are delegatable, user centricity will be more feasible in SOA. The credential-focused system is a good starting point for constructing a universal identity management system. However, how to implement a practical delegation scheme is still a challenge although there are some delegatable anonymous credential schemes that were theoretically constructed. This paper aims to propose a practical delegation solution for universal identity management. For this, a pseudonym-based signature scheme is first designed where pseudonyms are self-generated and unlinkable for realizing user's privacy. Next, a proxy signature is presented with the pseudonyms as public keys where delegation can be achieved through certificate chains. Finally, the security of our scheme is analyzed and proved in the random oracle model.