3.1.4.1. Implement Entra ID Authentication with MSAL

First Principle: Entra ID authentication is the primary identity provider for secure, cloud-native applications on Azure, enabling single sign-on and centralized access control.

What It Is: "Entra ID authentication" is the process by which an application verifies the identity of a user or service against "Entra ID".

Visual: "MSAL Simplified Authentication"

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High-level steps to implement Entra ID authentication:

1. "Register the application" in "Entra ID" to obtain a client ID and redirect URI. This creates an identity for your application that "Entra ID" can recognize.
2. "Configure API permissions" in "Entra ID" to allow your app to access Microsoft Graph or other APIs as needed.
3. "Integrate MSAL (Microsoft Authentication Library)" into your application code. "MSAL" simplifies authentication by:
   • Handling user sign-in and consent.
   • Acquiring, caching, and refreshing tokens securely.
   • Supporting multiple "authentication flows" (e.g., authorization code, device code, client credentials).

Example: MSAL.js in a Single-Page Application (SPA):

import { PublicClientApplication } from "@azure/msal-browser";
const msalConfig = {
  auth: {
    clientId: "YOUR_CLIENT_ID", // The App ID from your Entra ID app registration
    authority: "https://login.microsoftonline.com/YOUR_TENANT_ID" // Your Entra ID tenant authority
  }
};
const msalInstance = new PublicClientApplication(msalConfig);

async function signIn() {
  try {
    const loginResponse = await msalInstance.loginPopup({ scopes: ["user.read"] }); // Requesting permission to read user profile
    console.log("Logged in:", loginResponse.account.username);
    // Use loginResponse.accessToken for subsequent API calls to Microsoft Graph or other protected resources
  } catch (error) {
    console.error(error);
  }
}

Common scenarios:

• "SPAs (Single-Page Applications)": Use "MSAL.js" for browser-based authentication and token management.
• "Web apps (server-side)": Use "MSAL.NET" or "MSAL for Node.js" to authenticate users and call APIs.
• "Mobile apps": Use "MSAL for iOS/Android" to enable native sign-in experiences.
• "Desktop apps": Use "MSAL.NET" for Windows/macOS authentication.

Scenario: You are building a new single-page application (SPA) that needs to allow users to sign in using their Entra ID accounts. After signing in, the SPA needs to securely call a backend API that requires an access token.

Reflection Question: How does integrating "MSAL (Microsoft Authentication Library)" into your application code fundamentally simplify Entra ID authentication, handling user sign-in, and acquiring/managing tokens, ensuring secure and standards-based authentication across various application types?

💡 Tip: Always use an official "MSAL library" for Entra ID authentication. It handles the complexities of OAuth 2.0 and OpenID Connect protocols, token caching, and refresh logic, which are difficult and error-prone to implement manually.