doc: Document testing for OAuth protected registry MCP servers

[JasonYeMSFT]

What does this PR do?

This PR documents the required authentication testing for Entra ID protected http registry MCP servers to help partners who want to add registry servers verify their authentication setup.

GitHub issue number?

[Link to the GitHub issue this PR addresses]

Pre-merge Checklist

• Required for All PRs
  • Read contribution guidelines
  • PR title clearly describes the change
  • Commit history is clean with descriptive messages (cleanup guide)
  • Added comprehensive tests for new/modified functionality
  • Created a changelog entry if the change falls among the following: new feature, bug fix, UI/UX update, breaking change, or updated dependencies. Follow the changelog entry guide
• For MCP tool changes:
  • One tool per PR: This PR adds or modifies only one MCP tool for faster review cycles
  • Updated servers/Azure.Mcp.Server/README.md and/or servers/Fabric.Mcp.Server/README.md documentation
  • Validate README.md changes running the script ./eng/scripts/Process-PackageReadMe.ps1. See Package README
  • For new or modified tool descriptions, ran ToolDescriptionEvaluator and obtained a score of 0.4 or more and a top 3 ranking for all related test prompts
  • For tools with new names, including new tools or renamed tools, update consolidated-tools.json
  • For renamed tools, follow the Tool Rename Checklist and tag the PR with the breaking-change label
  • For new tools associated with Azure services or publicly available tools/APIs/products, add URL to documentation in the PR description
• Extra steps for Azure MCP Server tool changes:
  • Updated command list in servers/Azure.Mcp.Server/docs/azmcp-commands.md
  • Ran ./eng/scripts/Update-AzCommandsMetadata.ps1 to update tool metadata in azmcp-commands.md (required for CI)
  • Updated test prompts in servers/Azure.Mcp.Server/docs/e2eTestPrompts.md
  • 👉 For Community (non-Microsoft team member) PRs:
    • Security review: Reviewed code for security vulnerabilities, malicious code, or suspicious activities before running tests (crypto mining, spam, data exfiltration, etc.)
    • Manual tests run: added comment /azp run mcp - pullrequest - live to run Live Test Pipeline

[Copilot]

Pull request overview

This PR updates contributor documentation to better describe how to configure and validate authentication for OAuth/Entra ID–protected external MCP registry servers used by the Azure MCP Server.

Changes:

• Expands the “Configuring External MCP Servers” section with additional registry.json fields for HTTP servers (title, toolPrefix, oauthScopes).
• Adds guidance on Entra ID authentication scenarios (user principal, service principal, OBO) for external HTTP registry servers.
• Updates the “Adding New External MCP Servers” instructions to point at the Azure MCP Server’s embedded registry.json location.

Show a summary per file

File	Description
CONTRIBUTING.md	Adds/adjusts documentation for external registry servers, including HTTP server metadata and Entra ID auth testing guidance.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 4