How Microsoft Entra ID Authentication Works in ASP.NET Core Apps

Microsoft Entra ID is a cloud-based Identity and Access Management service that lets ASP.NET Core applications delegate user authentication to Microsoft, so the app never handles passwords directly. The authentication flow relies on OpenID Connect for verifying user identity and OAuth 2.0 for authorizing API access, with users receiving an ID Token and an Access Token after signing in. Developers must register their application in Microsoft Entra ID to obtain a Client ID, Tenant ID, Redirect URI, and Client Secret before configuring the app. The Microsoft.Identity.Web NuGet package simplifies implementation by handling the authorization code flow, token acquisition, and caching automatically. Most common issues encountered during setup stem from configuration mistakes such as redirect URI mismatches or incorrect tenant settings rather than coding errors.