Cross-Tenant Synchronization in Azure Active Directory: A Comprehensive Guide

Below are the steps that need to be performed to synchronize user and group information between on-premises Active Directory and Azure AD using Azure AD Connect.

1. Download and install Azure AD Connect on a server in your on-premises environment.
2. During the installation process, you will be prompted to sign in to your Azure AD tenant and provide credentials for an account that has permission to manage directory objects in Azure AD.
3. Next, you will be prompted to select the synchronization method. Choose the option that best fits your scenario. For example, if you have a single forest with a single domain, you can use the Express Settings.
4. After selecting the synchronization method, you will be prompted to configure the source and destination directories. This involves specifying the Active Directory domain that you want to synchronize, as well as the Azure AD tenant and directory that you want to synchronize with.
5. You will then be prompted to specify which objects you want to synchronize. This includes user accounts, groups, and optionally, devices.
6. After completing the configuration, Azure AD Connect will synchronize the specified objects from on-premises Active Directory to Azure AD. You can monitor the synchronization status and troubleshoot issues using the Azure AD Connect synchronization service manager.

Once the synchronization is complete, you can manage your users and groups in Active Directory and have those changes automatically reflected in Azure AD. This enables you to use a single identity and access management system for both on-premises and cloud-based resources.

Another simple example for Azure AD Graph API to synchronize users across multiple tenants is as follows:

• Register your application with Azure AD in both the source and target tenants. To do this, go to the Azure portal and navigate to Azure Active Directory > App registrations. Click the New registration button and follow the prompts to register your application. Make note of the application ID and secret for each registration.
• Grant the necessary permissions to your application in both the source and target tenants. To do this, navigate to the API permissions section of your application registration and add the required permissions.
• Generate an access token for the source tenant. To do this, you'll need to use the client ID and secret of your source tenant application registration. You can use the following code to generate an access token:

  public static async Task<string> GetAccessToken(string tenantId, string clientId, string clientSecret)
  {
      var authContext = new AuthenticationContext("https://login.microsoftonline.com/" + tenantId);
      var credential = new ClientCredential(clientId, clientSecret);
      var result = await authContext.AcquireTokenAsync("https://graph.windows.net", credential);
      return result.AccessToken;
  }

• Use the Azure AD Graph API to retrieve a list of users from the source tenant. You can use the following code to do this:

  public static async Task<IEnumerable<User>> GetUsers(string sourceTenantId, string sourceClientId, string sourceClientSecret)
  {
      var token = await GetAccessToken(sourceTenantId, sourceClientId, sourceClientSecret);
      var graphClient = new GraphServiceClient(
          new DelegateAuthenticationProvider((requestMessage) =>
          {
              requestMessage.Headers.Authorization = new AuthenticationHeaderValue("bearer", token);
              return Task.FromResult(0);
          }));
  
      var users = await graphClient.Users.Request().GetAsync();
      return users;
  }

• Use the Azure AD Graph API to create or update users in the target tenant. You can use the following code to do this:

  public static async Task CreateUser(string targetTenantId, string targetClientId, string targetClientSecret, User user)
  {
      var token = await GetAccessToken(targetTenantId, targetClientId, targetClientSecret);
      var graphClient = new GraphServiceClient(
          new DelegateAuthenticationProvider((requestMessage) =>
          {
              requestMessage.Headers.Authorization = new AuthenticationHeaderValue("bearer", token);
              return Task.FromResult(0);
          }));
  
      var existingUser = await graphClient.Users[user.UserPrincipalName].Request().GetAsync();
      if (existingUser == null)
      {
          await graphClient.Users.Request().AddAsync(user);
      }
      else
      {
          existingUser.GivenName = user.GivenName;
          existingUser.Surname = user.Surname;
          existingUser.UserPrincipalName = user.UserPrincipalName;
          await graphClient.Users[existingUser.Id].Request().UpdateAsync(existingUser);
      }
  }

• Call the GetUsers method to retrieve a list of users from the source tenant.
• For each user in the list, call the CreateUser method to create or update the user in the target tenant.

Following the above sequence you should now be able to use the Azure AD Graph API to synchronize users across multiple tenants. Of course, you may need to customize this code to suit your specific requirements, but this should provide a good starting point.

Topologies for cross-tenant synchronization

There are several topologies that can be used to implement cross-tenant synchronization in Azure AD, depending on the specific needs of the organization. Here are some of the most common topologies:

• One-way synchronization: In this topology, data is synchronized in one direction only, from the source tenant to the target tenant. This can be useful when one tenant contains authoritative data, and the other tenants need to consume that data.
• Two-way synchronization: In this topology, data is synchronized bidirectionally between the source and target tenants. This can be useful when multiple tenants need to update data, and all changes must be kept in sync.
• Hub-and-spoke: In this topology, one tenant acts as a hub, and all other tenants synchronize with it. This can be useful when there is a central organization that needs to distribute data to multiple subsidiaries or partner organizations.
• Mesh: In this topology, all tenants synchronize with each other, forming a network of interconnected tenants. This can be useful when there is a need for frequent data sharing between all tenants.

When choosing a topology, it's important to consider factors such as the size and complexity of the organization, the amount of data that needs to be synchronized, and the level of control required over data sharing between tenants.

Conclusion

Implementing cross-tenant synchronization in Azure AD can be a complex task, but it's an important part of managing multi-tenant organizations. By using the tools and services provided by Azure AD, you can synchronize user and group information between multiple tenants and ensure that all user information is consistent and up-to-date. Whether you choose to use Azure AD Connect, Azure AD B2B Collaboration, the Azure AD Graph API, Azure AD PowerShell, or Azure AD Connect Health, it's important to carefully plan and test your synchronization strategy before implementing it in a production environment.