User-centric services present a new paradigm in next generation networks. The IP Multimedia Subsystem (IMS) is an access-independent IP based service control architecture proposing a new platform for user-centric services. Security and data privacy aspects observe a lot of attention in the IMS global objectives. Besides the authentication solutions proposed by the third Generation Partnership Project (3GPP), research contributions consider authentication protocols and mechanisms to enforce the security and to enhance users' access personalization for IMS based services. Performance is an important factor to be considered when designing authentication protocols. In this paper we use Open BCMP queuing network as a mathematical model to evaluate the performance of an authentication method aiming to personalize each user access. We also propose an algorithm based on clustering to improve the performance of the authentication solution. Through BCMP modeling, we present and analyze the performance of the proposed authentication solution as a first step, and then we show the performance improvement of this solution when applying the clustering algorithm.