Entra App Registration

## Overview

Microsoft Entra ID (formerly Azure Active Directory) is Microsoft's cloud-based identity and access management service. App registrations allow applications to authenticate users and access Azure resources securely.

### Key Concepts

| Concept | Description |
|---------|-------------|
| **App Registration** | Configuration that allows an app to use Microsoft identity platform |
| **Application (Client) ID** | Unique identifier for your application |
| **Tenant ID** | Unique identifier for your Azure AD tenant/directory |
| **Client Secret** | Password for the application (confidential clients only) |
| **Redirect URI** | URL where authentication responses are sent |
| **API Permissions** | Access scopes your app requests |
| **Service Principal** | Identity created in your tenant when you register an app |

### Application Types

| Type | Use Case |
|------|----------|
| **Web Application** | Server-side apps, APIs |
| **Single Page App (SPA)** | JavaScript/React/Angular apps |
| **Mobile/Native App** | Desktop, mobile apps |
| **Daemon/Service** | Background services, APIs |

## Core Workflow

### Step 1: Register the Application

Create an app registration in the Azure portal or using Azure CLI.

**Portal Method:**
1. Navigate to Azure Portal → Microsoft Entra ID → App registrations
2. Click "New registration"
3. Provide name, supported account types, and redirect URI
4. Click "Register"

**CLI Method:** See [references/cli-commands.md](references/cli-commands.md)
**IaC Method:** See [references/BICEP-EXAMPLE.bicep](references/BICEP-EXAMPLE.bicep)

It's highly recommended to use the IaC to manage Entra app registration if you already use IaC in your project, need a scalable solution for managing lots of app registrations or need fine-grained audit history of the configuration changes. 

### Step 2: Configure Authentication

Set up authentication settings based on your application type.

- **Web Apps**: Add redirect URIs, enable ID tokens if needed
- **SPAs**: Add redirect URIs, enable implicit grant flow if necessary
- **Mobile/Desktop**: Use `http://localhost` or custom URI scheme
- **Services**: No redirect URI needed for client credentials flow

### Step 3: Configure API Permissions

Grant your application permission to access Microsoft APIs or your own APIs.

**Common Microsoft Graph Permissions:**
- `User.Read` - Read user profile
- `User.ReadWrite.All` - Read and write all users
- `Directory.Read.All` - Read directory data
- `Mail.Send` - Send mail as a user

**Details:** See [references/api-permissions.md](references/api-permissions.md)

### Step 4: Create Client Credentials (if needed)

For confidential client applications (web apps, services), create a client secret, certificate or federated identity credential.

**Client Secret:**
- Navigate to "Certificates & secrets"
- Create new client secret
- Copy the value immediately (only shown once)
- Store securely (Key Vault recommended)

**Certificate:** For production environments, use certificates instead of secrets for enhanced security. Upload certificate via "Certificates & secrets" section.

**Federated Identity Credential:** For dynamically authenticating the confidential client to Entra platform.

### Step 5: Implement OAuth Flow

Integrate the OAuth flow into your application code.

**See:**
- [references/oauth-flows.md](references/oauth-flows.md) - OAuth 2.0 flow deta