Office 365 Development: Microsoft Graph API Basics

Microsoft Graph is the gateway to Office 365 data. Users, emails, calendars, files—it’s all accessible through one unified API. Here’s how to get started.

What is Microsoft Graph?

Graph is a REST API that provides access to Microsoft 365 services. Instead of separate APIs for SharePoint, Exchange, Teams, etc., you use one endpoint: https://graph.microsoft.com

Authentication

Graph uses OAuth 2.0. You need to register an app in Azure AD:

1. Go to Azure Portal → Azure Active Directory → App registrations
2. Create new registration
3. Add API permissions (e.g., User.Read, Mail.Read)
4. Get your Client ID and create a Client Secret

Making Your First Call

// Using Microsoft.Graph NuGet package
var scopes = new[] { "User.Read" };
var clientId = "your-client-id";
var tenantId = "your-tenant-id";

var credential = new InteractiveBrowserCredential(tenantId, clientId);
var graphClient = new GraphServiceClient(credential, scopes);

// Get current user
var me = await graphClient.Me.Request().GetAsync();
Console.WriteLine($"Hello, {me.DisplayName}!");

Common Operations

// Get user's emails
var messages = await graphClient.Me.Messages
    .Request()
    .Top(10)
    .Select("subject,from,receivedDateTime")
    .GetAsync();

// Get user's calendar events
var events = await graphClient.Me.Events
    .Request()
    .Filter("start/dateTime ge '2019-03-01'")
    .GetAsync();

// Get files from OneDrive
var files = await graphClient.Me.Drive.Root.Children
    .Request()
    .GetAsync();

Graph Explorer

Before writing code, test queries in the Graph Explorer: https://developer.microsoft.com/graph/graph-explorer

It’s invaluable for understanding response shapes and testing permissions.

Permissions

Graph uses granular permissions:

• Delegated: User signs in, app acts on their behalf
• Application: App acts as itself (daemon/service)

Always request the minimum permissions needed.

References

• Microsoft Graph Overview
• Graph Explorer