What is a Tenant ID?

A Tenant ID is a globally unique identifier (GUID) that represents an organization (tenant) in a cloud identity system such as Microsoft Entra ID (formerly Azure Active Directory).

Think of it as:

Country -> State -> City -> Tenant -> Users

or

Microsoft Cloud
       |
       +---- Tenant A (Company A)
       |
       +---- Tenant B (Company B)
       |
       +---- Tenant C (Company C)

Each tenant receives a unique Tenant ID.

Example:

Tenant Name: Contoso Ltd

Tenant ID: 72f988bf-86f1-41af-91ab-2d7cd011db47

What is a Tenant?

A tenant is an isolated container that stores:

Users
Groups
Applications
Roles
Permissions
Policies
Licenses
Devices

Example:

Microsoft Entra ID

Tenant A
    Users:
        John
        David
        Admin
Tenant B
    Users:
        Alice
        Bob
Tenant C
    Users:
        Smith

Data is isolated between tenants.

Why Tenant ID Exists

Without Tenant IDs:

John from Company A
John from Company B

How does Microsoft know which company?

Using Tenant IDs:

Tenant A
    John

Tenant B
    John

The Tenant ID uniquely identifies the organization.

Tenant ID Format

A Tenant ID is always a GUID.

Example:

f8cdef31-a31e-4b4a-93e4-5f571e91255a

Length:

36 characters

Pattern:

xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Where is Tenant ID Used?

Authentication

When users log in:

User Login
      |
      v
Tenant ID
      |
      v
Find Organization
      |
      v
Authenticate User

Application Registration

Example:

Taxi Booking Admin Portal

Application belongs to:

Tenant:
Contoso

Tenant ID:72f988bf-86f1-41af-91ab-2d7cd011db47

API Security

When calling APIs:

GET api/bookings

Authorization: Bearer Token

Token contains:

{
   "tid": "72f988bf-86f1-41af-91ab-2d7cd011db47"
}

tid = Tenant ID

Multi-Tenant Applications

Example:

SaaS CRM Application

Customers:

TCS
Infosys
Wipro
Accenture

Each customer gets:

Different Tenant ID

Used to separate data.

Tenant ID vs Subscription ID

Many developers confuse these.

Tenant ID

Represents:

Identity Organization

Contains:

Users
Groups
Applications

Example:

72f988bf-86f1-41af-91ab-2d7cd011db47

Subscription ID

Represents:

Billing Account

Contains:

VMs
Databases
Storage

Example:

b9dc1c45-df2a-48a1-8f4b-5d8f462b9ab7

Relationship:

Tenant
     |
     +------- Subscription 1
     |
     +------- Subscription 2
     |
     +------- Subscription 3

One tenant can have multiple subscriptions.

Tenant ID vs Client ID

Another common confusion.

Tenant ID

Organization

Example:

Contoso

Client ID

Application

Example:

Taxi Booking Portal

Diagram:

Tenant
|
+---- Application A
|      Client ID
|
+---- Application B
|      Client ID
|
+---- Application C
       Client ID

Single Tenant Application

Only one organization can use it.

Contoso Only

Authentication URL:

https://login.microsoftonline.com/{tenant-id}/oauth2/v2.0/token

Example:

https://login.microsoftonline.com/72f988bf-86f1-41af-91ab-2d7cd011db47/oauth2/v2.0/token

Multi-Tenant Application

Many organizations can use it.

Example:

Salesforce
GitHub Enterprise
ServiceNow

Flow:

Company A
Company B
Company C
      |
      v
Multi-Tenant App

Tenant ID in JWT Token

When authentication succeeds:

{
  "aud": "api://taxi-app",
  "iss": "https://login.microsoftonline.com/",
  "tid": "72f988bf-86f1-41af-91ab-2d7cd011db47",
  "sub": "123456789",
  "name": "John Doe"
}

Useful for:

Authorization
User Isolation
Data Segregation
Auditing

Multi-Tenant SaaS Example

Suppose you build:

Taxi Fleet Management Platform

Customers:

Uber Fleet
Ola Fleet
Rapido Fleet

Database:

Companies
---------
CompanyId
TenantId
Name

Bookings
---------
BookingId
TenantId
CustomerId

Every query uses:

WHERE TenantId = @TenantId

This prevents customers from seeing each other's data.

Finding Tenant ID

Azure Portal

Azure Portal

→ Microsoft Entra ID
→ Overview
→ Tenant ID

Example:

Directory (Tenant) ID:
72f988bf-86f1-41af-91ab-2d7cd011db47

Azure CLI

az account show

Result:

{
  "tenantId": "72f988bf-86f1-41af-91ab-2d7cd011db47"
}

PowerShell

Get-AzTenant

Why is Tenant ID Important?

Used for:

• ✓ Authentication
• ✓ Authorization
• ✓ User Management
• ✓ SSO (Single Sign-On)
• ✓ Multi-Tenant SaaS
• ✓ Security Boundaries
• ✓ API Access Control
• ✓ Subscription Management
• ✓ B2B Collaboration
• ✓ Identity Federation
• ✓ Auditing
• ✓ Compliance

C# Example

Reading the Tenant ID from a JWT token in an ASP.NET Core API:

using Microsoft.AspNetCore.Mvc;
using System.Security.Claims;

[ApiController]
[Route("api/[controller]")]
public class BookingController : ControllerBase
{
    [HttpGet]
    public IActionResult GetBookings()
    {
        string tenantId = User.FindFirst("tid")?.Value;
        return Ok(new
        {
            Message = "Tenant identified successfully",
            TenantId = tenantId
        });
    }
} 

Example JWT:

    {
    "tid": "72f988bf-86f1-41af-91ab-2d7cd011db47",
    "name": "John Doe"
    }

    //Output:
    {
    "message": "Tenant identified successfully",
    "tenantId": "72f988bf-86f1-41af-91ab-2d7cd011db47"
    }

Real-world SaaS usage

var tenantId = User.FindFirst("tid")?.Value;

var bookings = await _dbContext.Bookings
    .Where(x => x.TenantId == tenantId)
    .ToListAsync();

This ensures that users only access data belonging to their own organization, which is the primary purpose of a Tenant ID in multi-tenant cloud applications.