Modernizing Legacy SSO with Microsoft Entra, Protect On-Prem Apps Without Rewriting Code

Enterprise legacy applications relying on identity platforms like SiteMinder or PingFederate can be modernized without code rewrites by using Microsoft Entra Application Proxy with header-based SSO. This approach preserves existing HTTP header authentication contracts (e.g., SM_USER, SM_ROLE) while migrating the identity control plane to Entra, enabling organizations to retire costly legacy IAM licensing. The key insight is that if the header contract remains unchanged, the application itself needs no modification.