Add comprehensive guide for configuring Microsoft Entra ID as OIDC provider for Apicurio Registry 3.1

[EricWittmann]

Summary

• Added comprehensive guide for securing Apicurio Registry 3.1 with Microsoft Entra ID External Tenants
• Document covers OIDC configuration, tenant setup, application registration, role-based authorization, and troubleshooting
• Includes step-by-step instructions with detailed environment variable configurations and machine-to-machine authentication setup

Description

This guide provides detailed instructions for replacing Keycloak with Microsoft Entra ID External Tenants as an identity provider for Apicurio Registry 3.1.0. The document covers critical configuration differences between Entra ID and Keycloak, particularly around JWT token structure and the roles claim.

Key topics covered:

• Microsoft Entra ID External tenant creation and configuration
• Application registration with proper OIDC settings
• App roles configuration for sr-admin, sr-developer, and sr-readonly
• Complete environment variable reference
• Client credentials grant flow for service-to-service authentication
• Common issues and troubleshooting tips

Test Plan

• Verify the guide is accessible at docs/guides/2025/securing-apicurio-registry-with-microsoft-entra-id-external-tenants.md
• Review content for accuracy and completeness
• Confirm markdown formatting renders correctly
• Validate that all code snippets and configuration examples are properly formatted