[Issue]: Validate Entra ID tokens in the API #8

Branch Name

feature/08-token-api

Task

Description
Configure the ASP.NET Core API to accept and validate Entra ID access tokens, so that only authenticated users can reach protected endpoints.

Scope

• JWT bearer authentication in ASP.NET Core
• Validate issuer, audience and signature
• Protect the API endpoints by default
• Add a test endpoint that returns the current user

Acceptance Criteria

• A request with a valid token succeeds
• A request without a token returns 401
• A request with an invalid or expired token returns 401

Checklist

• I have checked for duplicate issues.
• I have assigned the issue to the correct project board.
• I have tagged the issue properly.

Code of Conduct

• I agree to follow this project's Code of Conduct