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How do I get an Entra-joined privately networked Azure compute resource able to write files to an on-prem-Azure-Directory-joined on-prem-networked Windows Server acting as a DFS (Distributed File System) namespace

To enable an Entra-joined Azure compute resource to write files to an on-premises Windows Server acting as a DFS namespace, follow these steps:

1. Establish Network Connectivity

• Use a Site-to-Site VPN or Azure ExpressRoute to securely connect your Azure Virtual Network (VNet) with the on-premises network¹².
• Ensure proper DNS resolution between the Azure VNet and the on-premises environment³.

2. Configure Access to On-Prem Resources

• Enable Microsoft Entra Private Access for secure communication without requiring a VPN, if applicable⁴⁵.
• Ensure the Entra-joined device has line-of-sight to the on-premises Active Directory (AD) and file server⁶⁷.

3. Authentication Configuration

• Use Kerberos authentication by syncing Entra ID with on-prem AD through Azure AD Connect. This enables Single Sign-On (SSO) for accessing on-prem resources from Entra-joined devices⁶⁸.
• Verify that the Entra ID user account exists in the on-prem AD and has necessary permissions for the DFS namespace⁶.

4. Setup DFS Namespace Integration

• On the Windows Server hosting DFS:
  • Add Azure File Shares as folder targets in your DFS namespace if hybrid integration is needed⁹¹⁰.
  • Ensure proper ACLs (Access Control Lists) are maintained during setup.

5. Testing and Validation

• Test file write operations from the Azure compute resource to ensure proper access.
• Use tools like klist to confirm Kerberos tickets are issued for SMB access⁶.

This configuration enables seamless and secure file sharing between your Azure and on-prem environments.

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How would I ensure that a nonhuman Entra service principal can correspond to the on-prem-Active-Directory account? Is that even a thing?

It is not possible to directly synchronize a Microsoft Entra service principal (SP) with an on-premises Active Directory (AD) account because service principals are specific to Microsoft Entra ID and are not designed to map to on-prem AD objects. However, there are workarounds to enable similar functionality:

Options for Correspondence Between Entra Service Principals and On-Prem AD

1. Use a Group Managed Service Account (gMSA):
   • Create a gMSA in the on-prem AD to act as the identity for accessing resources.
   • Assign necessary permissions to the gMSA for interacting with on-prem systems¹¹.
2. Create a Dedicated User Account in On-Prem AD:
   • Manually create a user account in the on-prem AD that corresponds to the service principal.
   • Use this account for authentication when accessing on-prem resources. Sync this account with Microsoft Entra ID using Azure AD Connect¹²¹¹.
3. Leverage Azure AD Domain Services (AADDS):
   • AADDS can provide LDAP and Kerberos support for legacy applications.
   • However, AADDS does not synchronize service principals—only user accounts and groups are synced. You would need to use a workaround like creating a user account¹¹.
4. Custom Attribute Mapping via API-Driven Provisioning:
   • If you need specific attributes or mappings, use API-driven provisioning to customize how attributes from Entra ID are mapped to on-prem AD accounts¹³.

Key Considerations

• Service principals are primarily for application authentication in cloud environments and do not naturally integrate with traditional on-prem AD environments.
• For hybrid scenarios, use user accounts or gMSAs as proxies for service principals when accessing on-prem resources.

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How does a gMSA help? Do they automatically also exist in Entra? I don’t get it.

A Group Managed Service Account (gMSA) helps by providing a secure, automated, and domain-managed identity for services or applications running on servers. Here’s how it works and why it doesn’t directly exist in Entra ID:

How a gMSA Helps

1. Automated Password Management: The gMSA’s password is automatically managed and rotated by the Active Directory (AD), eliminating manual password handling and reducing security risks¹⁴¹⁵.
2. Domain-Wide Access: A gMSA can be used across multiple servers in the same AD domain, making it ideal for services like DFS or applications that require consistent credentials across a server farm¹⁴¹⁶.
3. Kerberos Authentication: gMSAs support Kerberos, enabling secure authentication to on-premises resources without requiring hardcoded passwords¹⁴¹⁷.

Do gMSAs Exist in Microsoft Entra ID?

No, gMSAs are strictly an on-premises Active Directory feature. They do not exist in Microsoft Entra ID because:

• Entra ID uses service principals for application authentication, which are cloud-native and do not rely on traditional AD mechanisms like Kerberos or NTLM.
• Password management for service principals is handled differently (e.g., certificates or client secrets), not via AD’s Key Distribution Service (KDS)¹⁸¹⁹.

Workaround for Hybrid Scenarios

To bridge the gap between an Entra service principal and an on-premises AD resource:

1. Use a gMSA Locally:
   • Create a gMSA in your on-prem AD for the service or application.
   • Assign it permissions to access the DFS namespace or other resources.
2. Proxy Authentication:
   • Configure your Azure-hosted application to authenticate indirectly with the gMSA by using a hybrid identity solution like Azure AD Connect or Entra Cloud Sync²⁰¹⁹.
   • Alternatively, deploy a domain-joined VM in Azure that uses the gMSA to access the on-prem resource.

Key Takeaway

gMSAs are powerful for securing on-premises services but cannot directly map to Entra service principals. For hybrid scenarios, use domain-joined resources or custom solutions to bridge the identity gap.

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What’s a domain-joined Azure VM? How does that help it use on-prem AD?

A domain-joined Azure VM is a virtual machine in Azure that is joined to an Active Directory (AD) domain, either on-premises or Azure-based. This allows the VM to use traditional AD services like Kerberos, NTLM, and Group Policy for authentication and management.

How It Helps Use On-Premises AD

1. Authentication: A domain-joined Azure VM can authenticate to on-prem AD just like any other domain-joined machine in your network.
2. Access to On-Prem Resources: The VM can access file shares, DFS namespaces, and other resources that require AD credentials.
3. Centralized Management: You can manage the VM with on-prem Group Policies (GPOs), ensuring consistent security and configuration.

Steps to Join an Azure VM to On-Prem AD

1. Establish Network Connectivity:
   • Set up a VPN or ExpressRoute between your Azure Virtual Network (VNet) and the on-premises network.
   • Ensure proper DNS resolution by configuring the Azure VNet to use your on-prem DNS servers.
2. Provision the Azure VM:
   • Deploy the VM in the same VNet connected to your on-prem network.
   • Ensure it has no public IP for security and uses a private IP address.
3. Join the Domain:
   • Configure the VM’s DNS settings to point to your on-prem DNS servers.
   • Use the traditional domain join process (System Properties > Change Settings > Domain), providing valid AD credentials.
4. Authentication and Access:
   • Once joined, the VM can authenticate users and services against the on-prem AD.
   • Use AD accounts or service accounts for accessing resources like DFS.

Alternative: Azure AD Domain Services (AAD DS)

If you don’t want to rely on a VPN or extend your on-prem AD, you can use Azure AD Domain Services (AAD DS). AAD DS provides managed domain controllers in Azure that support domain joining, Kerberos, NTLM, and LDAP without requiring you to manage traditional AD infrastructure²¹²²²³.

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What about plain old certificates or secrets? The Azure VM can be configured to have one of them on file. Would that help with authentication into on-prem-AD-protected resources at all?

Using certificates or secrets on an Azure VM can help with authentication to on-premises AD-protected resources, but only indirectly. Here’s how they might work and their limitations:

How Certificates or Secrets Can Help

1. Service Principal with Secret/Certificate:
   • You can configure an Azure service principal with a client secret or certificate and store these credentials securely in Azure Key Vault.
   • The Azure VM can retrieve these credentials using its managed identity and use them to authenticate to applications or services that accept the service principal’s credentials.
2. On-Prem AD Authentication:
   • If your on-prem AD-protected resource supports certificate-based authentication (e.g., via LDAP over SSL) or explicit credentials, you can use the retrieved secret/certificate for access.
   • For example, you could store the credentials of an on-prem AD service account in Key Vault and retrieve them from the Azure VM to authenticate to the AD-protected resource.
3. Azure Key Vault as a Credential Store:
   • You can store on-prem AD credentials (e.g., username/password of a service account) in Key Vault.
   • The Azure VM retrieves these credentials and uses them for authentication to the on-prem AD-protected resource.

Limitations

• No Direct Integration: On-prem AD does not natively support Azure service principals or managed identities. You must use a proxy mechanism (e.g., service accounts or certificates) for authentication.
• Manual Configuration: You need to manually configure on-prem resources to accept certificate-based authentication or explicit credentials.
• Security Risks: Using secrets introduces potential risks if not managed properly, even when stored in Key Vault.

Steps for Implementation

1. Create a Service Principal and Secret/Certificate:
   • Register an application in Microsoft Entra ID and generate a client secret or upload a certificate.
2. Store Credentials in Azure Key Vault:
   • Add the secret/certificate to Key Vault and grant the Azure VM’s managed identity access to retrieve it.
3. Configure On-Prem Resource for Authentication:
   • If using certificates, configure your on-prem AD-protected resource (e.g., LDAP server) to accept certificate-based authentication.
   • If using explicit credentials, ensure the corresponding on-prem AD account has appropriate permissions.
4. Retrieve Credentials from Key Vault:
   • Use the Azure VM’s managed identity to securely fetch the secret/certificate from Key Vault.
5. Authenticate to On-Prem Resource:
   • Use the retrieved credentials (e.g., via PowerShell or application code) to authenticate against the on-prem AD-protected resource.

Key Takeaway

While certificates or secrets can help bridge authentication gaps, they require additional configuration and do not provide native integration with on-prem AD. For seamless access, consider hybrid identity solutions like domain-joined VMs or Azure AD Connect with synchronized accounts.

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Sooooo… on-prem-AD identities can be always signed into merely by secret/certificate?

Yes, on-premises Active Directory (AD) can support authentication using certificates, but it requires specific configurations and is not as straightforward as using passwords or Kerberos. Here’s an overview:

Certificate-Based Authentication in AD

1. Certificate Mapping:
   • Certificates can be mapped to AD user accounts using attributes like altSecurityIdentities or userCertificate²⁴²⁵²⁶.
   • This mapping allows the certificate to act as a credential for the user.
2. Authentication Process:
   • The user or device presents an X.509 certificate to the AD domain controller.
   • The domain controller validates the certificate against its trusted Certificate Authority (CA) and checks the mapping to an AD account²⁵²⁷.
3. Requirements:
   • A Certificate Authority (CA), such as Active Directory Certificate Services (AD CS), must issue the certificates²⁸²⁷.
   • Domain controllers must be configured to support certificate-based authentication, including enabling smart card logon or TLS mutual authentication²⁶²⁷.
4. Use Cases:
   • Commonly used for smart card logon, Wi-Fi access, VPNs, or other scenarios where passwordless authentication is preferred²⁸²⁶.

Limitations

• Mapping Complexity: Certificates must be explicitly mapped to user accounts, which can be time-consuming and error-prone.
• Protocol Support: Certificate-based authentication is typically used with protocols like LDAP over SSL/TLS or smart card logon, not directly with Kerberos or NTLM²⁹³⁰.
• Infrastructure Dependency: Requires a robust PKI setup and proper configuration of domain controllers and clients.

Key Takeaway

While certificates can authenticate users or devices in on-prem AD, they are not a universal replacement for traditional methods like Kerberos. Instead, they complement existing mechanisms in specific scenarios where stronger security or passwordless authentication is needed.

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What would the Azure VM have to do to be able to authenticate itself over Kerberos?

To enable an Azure VM to authenticate itself over Kerberos, it must be domain-joined to an Active Directory (AD) domain. This process allows the VM to interact with on-premises AD for Kerberos-based authentication. Here’s how it works and the steps involved:

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How Kerberos Authentication Works for Azure VMs

• Kerberos requires the VM to be part of an AD domain so it can obtain a Kerberos ticket from a Key Distribution Center (KDC), typically hosted on an on-premises domain controller.
• The VM must have line-of-sight to the KDC, which is achieved via network connectivity, DNS configuration, and proper domain joining.

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Steps to Enable Kerberos Authentication

1. Establish Network Connectivity:
   • Set up a VPN or Azure ExpressRoute to connect your Azure Virtual Network (VNet) to the on-premises network.
   • Ensure DNS resolution for the on-prem AD domain by configuring the Azure VNet to use your on-prem DNS servers.
2. Join the VM to the On-Prem AD Domain:
   • Configure the Azure VM’s DNS settings to point to your on-prem DNS servers.
   • Join the VM to the domain using standard Windows domain join procedures:
     • Open System Properties > Change Settings > Domain.
     • Enter the on-prem AD domain name and provide credentials of a user with permissions to join devices to the domain³¹³².
3. Configure Kerberos Authentication:
   • Once joined, the VM will automatically use Kerberos for authentication when accessing resources in the same AD domain.
   • Use tools like klist on the VM to verify that Kerberos tickets are being issued.
4. Validate Access:
   • Test access to on-prem AD-protected resources (e.g., file shares, DFS namespaces) using Kerberos authentication.
   • Ensure proper permissions are configured in AD for the VM or service accounts running on it.

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Key Considerations

• Line-of-Sight: The VM must have uninterrupted network connectivity to the on-premises domain controllers for Kerberos ticket issuance and validation.
• DNS Configuration: Proper DNS resolution is critical for locating domain controllers and issuing Kerberos tickets.
• Hybrid Identity Options: If direct domain joining isn’t feasible, consider using Azure Active Directory Domain Services (AAD DS), which provides managed domain controllers in Azure that support Kerberos³³³².

By joining an Azure VM to an on-prem AD, it can fully participate in Kerberos authentication for secure access to resources.

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Can a Linux Azure VM be domain-joined?

Yes, a Linux Azure VM can be domain-joined, but it depends on the type of domain. Here are the key options:

1. Joining to Microsoft Entra Domain Services (AAD DS)

• Linux VMs can be joined to Microsoft Entra Domain Services (AAD DS), which provides managed domain services like LDAP, Kerberos, and NTLM.
• This allows the VM to use domain credentials for authentication and access control.
• Supported distributions include Ubuntu, Red Hat Enterprise Linux (RHEL), and others³⁴³⁵³⁶.

Steps:

1. Configure the Linux VM to communicate with the AAD DS-managed domain (e.g., set DNS to point to AAD DS).
2. Install tools like realmd, sssd, or adcli on the Linux VM.
3. Use commands like realm join or adcli join to join the domain³⁴³⁵.

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2. Joining to On-Premises Active Directory

• A Linux VM can also be joined to an on-premises AD domain using tools like SSSD, realmd, or Samba.
• This requires network connectivity (e.g., VPN or ExpressRoute) between Azure and the on-premises environment.

Steps:

1. Ensure DNS resolution for the on-prem AD domain by pointing the VM’s DNS settings to on-prem DNS servers.
2. Install necessary packages (realmd, sssd, etc.).
3. Use commands like realm join with on-prem AD credentials.

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3. Authentication via Azure AD (Without Domain Join)

• If domain join is not required, you can enable Azure AD-based authentication for Linux VMs using extensions like AADLoginForLinux.
• This method allows users to log in with their Azure AD credentials but does not provide traditional Kerberos or NTLM support³⁷³⁸.

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Key Considerations

• For Kerberos-based authentication, ensure that the domain (AAD DS or on-prem AD) supports Kerberos and is properly configured.
• AAD DS is simpler for Azure-native environments, while on-prem AD requires additional networking setup.

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