The evolution of enterprise Java applications has generated a profound tension between legacy security mechanisms and contemporary authentication frameworks. This study systematically examines the integration, adaptation, and comparative efficacy of OpenSAML, Spring Security, and JWT-based authentication, highlighting their respective impacts on software maintainability, performance, and enterprise-level security resilience. The research integrates theoretical foundations from security engineering, enterprise software modernization, and identity and access management, contextualized within large-scale application landscapes characterized by monolithic architectures transitioning to microservices and cloud-native deployments. By combining historical analyses of Java security paradigms with contemporary empirical evaluations, this study elucidates critical design considerations for organizations navigating the balance between technical debt mitigation and modern security adoption.

The methodology employed involves a structured qualitative analysis of existing frameworks, supplemented by a comprehensive review of case studies involving enterprise migrations, technical debt assessment, and microservice adoption patterns (Kathi, 2025; Somayajula, 2025). Findings suggest that while OpenSAML offers robust legacy SAML-based capabilities crucial for backward compatibility, Spring Security provides a flexible and extensible framework suited for complex enterprise requirements, and JWT-based mechanisms excel in lightweight, stateless authentication scenarios suitable for cloud-based and microservice architectures. Furthermore, the research identifies strategic pathways for mitigating integration challenges, enhancing security postures, and leveraging modernization opportunities to optimize both operational efficiency and compliance adherence.

The discussion contextualizes these insights within broader debates on enterprise modernization, highlighting trade-offs in security, scalability, and maintainability. Limitations include the absence of longitudinal deployment metrics and heterogeneity in organizational adoption practices, which constrain generalizability. Future research directions encompass empirical validation of hybrid authentication strategies, AI-driven security monitoring within modern Java applications, and comparative analyses of emergent authentication protocols under diverse enterprise conditions. This study contributes to a nuanced understanding of the interplay between legacy and contemporary security strategies, providing actionable guidance for software engineers, architects, and decision-makers aiming to modernize enterprise Java applications while preserving robust security standard.