Cross-Tenant Synchronization (CTS) with Azure B2B Collaboration and PowerShell

Introduction

Cross-Tenant Synchronization (CTS) allows organizations to securely sync users across Azure Active Directory (Azure AD) tenants for seamless B2B collaboration. Instead of manually managing external identities, CTS automates identity sharing, reduces administrative burden, and strengthens security.

In this guide, we’ll cover what CTS is, why it matters, and how you can configure it using real-world PowerShell examples.

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What is Cross-Tenant Synchronization (CTS)?

CTS enables organizations to automatically create and manage B2B collaboration users across tenants, ensuring updated identities and permissions without manual intervention. It facilitates external collaboration without compromising compliance or security.

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Why Use CTS for B2B Collaboration?

• Secure Identity Sharing: Automates user onboarding and offboarding between organizations.
• Unified Collaboration: Enables external users to access Teams, SharePoint, and other Microsoft 365 services.
• Simplified Management: Reduces manual directory maintenance and ensures identities stay updated.
• Compliance: Supports MFA and Conditional Access for external users.

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High-Level Setup Steps for CTS

1. Establish a trust relationship between the source and target Azure AD tenants.
2. Define synchronization rules for user attributes.
3. Configure B2B Collaboration settings.
4. Automate and manage policies with PowerShell.

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PowerShell Sample: Setting Up B2B Trust

# Step 1: Connect to Azure AD
Connect-AzureAD

# Step 2: Create a basic B2B Invitation Policy
New-AzureADPolicy \
  -Definition @('{"B2BInvitation": {"Enabled": true}}') \
  -DisplayName "CTS B2B Collaboration Policy" \
  -Type "B2BInvitationPolicy"

# Step 3: Set Cross-Tenant Access Policy for External Collaboration
Connect-MgGraph -Scopes "Policy.ReadWrite.CrossTenantAccess"

$policy = @{
    inboundTrust = @{ isMfaAccepted = $true; isCompliantDeviceAccepted = $true }
    outboundTrust = @{ isMfaAccepted = $true; isCompliantDeviceAccepted = $true }
}

Update-MgPolicyCrossTenantAccessPolicy -BodyParameter $policy

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Best Practices for Cross-Tenant Synchronization

• Enforce MFA: Require multi-factor authentication for all external users.
• Use Conditional Access: Protect sensitive apps and data.
• Attribute Filtering: Only sync necessary user attributes.
• Separation of Admin Rights: Do not grant external users privileged roles.
• Audit and Monitor: Regularly review cross-tenant policies and access logs.

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Conclusion

Cross-Tenant Synchronization (CTS) streamlines external collaboration without sacrificing security. Whether you’re preparing for mergers, managing strategic partnerships, or extending services to external clients, automating CTS setup using PowerShell ensures scalability, consistency, and security.

Implement CTS today and strengthen your organization’s B2B collaboration foundation.

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✨ Related: See my PowerShell Toolbox for essential automation scripts.

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