请用学术的语言重新表述下列文字并将其缩减为200字左右：开放融合的 5G 网络支持业务需求多样化、不同接入网络异构共存、多元终端海量连接等新特征这对移动通信网络的安全带来了严峻挑战。5G 网络重要的安全机制之一是在设备和网络之间实现相互认证建立会话密钥以保证后续的安全通信然而当前的认证机制仍然存在诸多问题例如认证流程单一固化、密钥生命周期管理不够灵活、海量设备并发接入场景下信令拥塞等无法应对不同业

5G networks, with their open and integrated nature, face severe security challenges due to diverse business requirements, heterogeneous access networks, and massive device connectivity. One important security mechanism in 5G is mutual authentication between devices and networks to establish session keys for secure communication. However, current authentication mechanisms have many problems, such as a rigid authentication process, inflexible key lifecycle management, and signaling congestion in scenarios with concurrent device access. To address these issues, this paper proposes a unified authentication framework based on spectral clustering and Access Class Barring schemes to provide customized authentication services and key management for heterogeneous terminals in multiple business scenarios. Furthermore, the paper also proposes an access authentication and key negotiation mechanism for massive device connectivity and a new switching authentication and key update mechanism. Simulation results show that the proposed mechanisms are secure and efficient, providing a feasible solution for secure and efficient authentication and key negotiation in 5G networks