Azure AD Authentication Documentation

Introduction to Azure AD Authentication

Azure Active Directory (Azure AD) is a cloud-based identity and access management service that helps your employees sign in to applications and resources located either on-premises or in the cloud. Azure AD provides robust authentication and authorization capabilities, enabling secure access to a wide range of services.

This documentation covers the core concepts, protocols, and flows used for authenticating users and applications with Azure AD. Understanding these components is crucial for building secure and modern applications that leverage Azure AD for identity management.

Key Concepts

Here are some fundamental concepts you'll encounter when working with Azure AD authentication:

Identity: Represents a user, application, or service principal that needs to be authenticated and authorized.
Authentication: The process of verifying the identity of a user or application.
Authorization: The process of granting or denying access to specific resources based on authenticated identity and permissions.
Tenant: A dedicated instance of Azure AD that represents an organization.
Application Registration: The process of registering your application with Azure AD to enable it to authenticate users and access resources.
Service Principal: An instance of an application object that exists in a specific Azure AD tenant. It represents a specific application's identity within that tenant.

Authentication Protocols

Azure AD supports industry-standard protocols for authentication and authorization.

OAuth 2.0

OAuth 2.0 is an authorization framework that enables applications to obtain limited access to user accounts on an HTTP service, such as Facebook or GitHub. It works by delegating user verification to an authorization server. Azure AD implements OAuth 2.0 to grant delegated access to protected resources.

OpenID Connect (OIDC)

OpenID Connect is an identity layer built on top of the OAuth 2.0 protocol. It allows clients to verify the identity of the end-user based on the authentication performed by an authorization server, as well as to obtain basic profile information about the end-user in an interoperable and REST-like manner. Azure AD uses OIDC to provide identity information to applications.

When you use OIDC with Azure AD, you typically get an ID Token, which is a JWT (JSON Web Token) containing claims about the authenticated user.

SAML

Security Assertion Markup Language (SAML) is an open standard for exchanging authentication and authorization data between parties, specifically between an identity provider and a service provider. Azure AD can act as an identity provider for SAML-based single sign-on (SSO) to enterprise applications.

Authentication Flows

Azure AD supports various authentication flows to cater to different application types and scenarios.

Authorization Code Flow

The Authorization Code Flow is a grant type used by confidential clients (applications that can securely store credentials, like web applications) to obtain an access token. It's a secure, two-step process involving redirecting the user to Azure AD for authentication and then exchanging an authorization code for tokens.

// Simplified Pseudocode for Authorization Code Flow
// 1. User is redirected to Azure AD login page
GET https://login.microsoftonline.com/{tenant}/oauth2/v2.0/authorize?
    client_id=YOUR_CLIENT_ID&
    response_type=code&
    redirect_uri=YOUR_REDIRECT_URI&
    scope=https://graph.microsoft.com/.default

// 2. After user logs in and consents, Azure AD redirects back with an authorization code
GET YOUR_REDIRECT_URI?code=AUTHORIZATION_CODE

// 3. Application exchanges the authorization code for tokens
POST https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token
    grant_type=authorization_code&
    client_id=YOUR_CLIENT_ID&
    client_secret=YOUR_CLIENT_SECRET&
    redirect_uri=YOUR_REDIRECT_URI&
    code=AUTHORIZATION_CODE

Client Credentials Flow

The Client Credentials Flow is used for server-to-server interactions where an application needs to access resources directly without user involvement. The application authenticates itself using its credentials (client ID and secret or certificate) to obtain an access token.

// Simplified Pseudocode for Client Credentials Flow
POST https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token
    grant_type=client_credentials&
    client_id=YOUR_CLIENT_ID&
    client_secret=YOUR_CLIENT_SECRET&
    scope=https://graph.microsoft.com/.default

On-Behalf-Of Flow

The On-Behalf-Of (OBO) flow is used when a service (a front-end web app, for example) needs to call another service (a back-end API) on behalf of a user. The calling service obtains an access token for the user from Azure AD and then passes that token to the downstream service.

Tokens and Claims

When a user or application is authenticated, Azure AD issues tokens. The primary types of tokens are:

Access Tokens: Used to access protected resources (APIs). They contain information about the client and the permissions granted.
ID Tokens: Used in OpenID Connect flows to verify the identity of the user and obtain basic profile information. They are JWTs.
Refresh Tokens: Used to obtain new access tokens when the current ones expire, without requiring the user to re-authenticate.

Tokens contain claims, which are pieces of information asserted about the subject (user or application). Examples include user ID, name, roles, and permissions. You can inspect JWT tokens using online tools or libraries to understand their contents.

Best Practices

To ensure secure and efficient authentication with Azure AD:

Always use HTTPS for all communication with Azure AD endpoints.
Prefer the Authorization Code Flow with PKCE for public clients (SPAs, mobile apps).
Securely store client secrets or use certificate-based authentication for confidential clients.
Implement token validation rigorously on the resource server.
Handle token expiration and refresh gracefully.
Use appropriate scopes and grant the least privilege necessary.
Consider implementing multi-factor authentication (MFA) for enhanced security.
Leverage Azure AD Conditional Access policies to enforce granular access controls.

Note: The specific endpoints and parameters might vary slightly depending on the Azure AD API version you are using. Always refer to the latest Azure AD documentation for the most up-to-date information.