msal-auth-code-flow

name	msal-auth-code-flow
description	Authorization Code Flow for web applications using MSAL.NET confidential client to sign in users and access APIs on their behalf
tags	["msal","auth-code","authorization-code","web-app","confidential-client","user-sign-in","redirect","consent"]

Authorization Code Flow Skill

Overview

Authorization Code Flow is used by web applications to authenticate users and obtain access tokens on their behalf.

When to Use

• Web applications with server-side backend
• Need to access user-scoped APIs
• User sign-in required
• Refresh tokens needed

Flow Steps

1. Redirect user to AAD login page
2. User logs in and consents to permissions
3. AAD returns authorization code to callback URL
4. Server exchanges code for token using confidential credentials
5. Token cached and used to access APIs

Agent Actions

Generate Code Snippet

Agent can show code snippets for each credential type:

• Standard Certificate: with-certificate.cs
• Certificate with SNI: with-certificate-sni.cs
• Federated Identity Credentials: with-federated-identity-credentials.cs

Setup Guidance

Reference appropriate credential setup:

• Certificate Setup
• Certificate with SNI
• Federated Identity Credentials

Example: Web Application with Certificate

// In controller's callback method
[HttpGet("auth/callback")]
public async Task HandleCallback(string code, string state)
{
    // See: with-certificate.cs for credential setup
    var app = ConfidentialClientApplicationBuilder
        .Create(clientId)
        .WithCertificate(cert)
        .WithAuthority($"https://login.microsoftonline.com/{tenantId}/v2.0")
        .WithRedirectUri("https://myapp.com/auth/callback")
        .Build();

    var result = await app.AcquireTokenByAuthorizationCode(
        new[] { "scope-uri" },
        code)
        .ExecuteAsync();

    // Result contains AccessToken, RefreshToken, ExpiresOn
}

Error Resolution

Refer to Troubleshooting Guide

Best Practices

• Use Token Caching Strategies for optimal token acquisition
• Implement Error Handling Patterns
• Store refresh tokens securely
• Use PKCE for native clients
• For advanced caching options including distributed caches for multi-instance deployments, see Token cache serialization documentation

Explain the Flow

1. Initiation: Redirect to https://login.microsoftonline.com/{tenant}/oauth2/v2.0/authorize?client_id=...&redirect_uri=...
2. User Action: User logs in and grants consent
3. Code Reception: AAD sends authorization code to redirect URI
4. Token Exchange: Server uses code + client credentials to get token
5. Token Usage: Token cached and used for API calls

Decision Help

Choose Auth Code Flow if:

• Building web application with server backend
• Need to access user resources with user consent
• Want to maintain long-lived sessions (using refresh tokens)

Avoid if:

• Building single-page app (use implicit/hybrid instead)
• Don't have secure backend for credentials