Tag Archives: SSO

Single Sign-On and Azure AD Connect Pass-Through Authentication

In my previous blogpost I discussed Azure AD Connect Pass-Through Authentication (PTA), how it works and how it can be configured. In that blogpost I did not enable Single Sign-On (SSO) and that was also the first comment I got, within one or two days. Enabling SSO and how it works it this blogpost’s topic.

Authentication flow

I already explained the authentication flow when using PTA. When accessing a service in Office 365 you are redirected to Azure AD, you enter your credentials and the credentials are placed in the Azure Service Bus. The Azure AD Connect server retrieves these credentials from the Service Bus and presents them to the on-premises Domain Controller. The result is returned to the service bus and you’re granted access, or denied when something is wrong of course.

image

So, what happens if you enable SSO in the Azure AD Connect wizard? Enabling SSO is just a matter of checking the Enable single sign-on checkbox in the Azure AD Connect wizard:

image

Note. I skipped most of the configuration steps since this is identical to the configuration steps in the previous blogpost.

During the Azure AD Connect wizard you also must enter your on-premises administrator credentials, these are needed to configure your on-premises Active Directory to enable SSO with PTA.

To be fair, it’s not true SSO as with federation (through ADFS), but it is seamless Single-Sign On (sSSO). When enabling SSO in the Azure AD Connect wizard, users only need to enter their logon name when accessing services in Office 365, for example with Outlook Web App:

image

When you are on a domain joined workstation that has access to a Domain Controller, you only have to select the appropriate user account. The password is automatically returned to Azure AD and if all is well you are granted access to Outlook Web App.

If you don’t want to select or enter a logon name you can also use domain hints. In combination with Outlook Web App you would use a URL like https://outlook.office.com/owa/contoso.com. If you do so your current credentials (again, on a domain joined workstation that has access to a Domain Controller) are automatically passed through and you are granted access.

Seamless Single-Sign On under the hood

But how does this sSSO actually work under the hood.

When enabling SSO in the Azure AD Connect wizard you have to enter your on-premises domain administrator account. This is used to create an additional computer object in Active Directory called AZUREADSSOACC.

image

This computer account is used to create a shared Kerberos key between your on-premises Active Directory and Azure Active Directory, needed for creating the sSSO experience.

During logon in this scenario, the following 8 steps occur:

image

  1. The client accesses a service in the Microsoft cloud, for example OWA via https://outlook.office.com/owa.
  2. The request is redirected from Office 365 to Azure Active Directory.
  3. Access is denied, and a 401 error is returned to the client.
  4. The client accesses a local Domain Controller and requests a Kerberos token.
  5. A Kerberos session ticket is returned to the client.
  6. The session ticket is presented to Azure Active Directory. Since Azure Active Directory has a shared ticket with your on-premises Active Directory is can generate a Kerberos token for the client to use.
  7. The Kerberos token is returned to the client
  8. The Kerberos token is presented to Office 365 and access is granted. The user can now start using OWA.

As you can see this only works for domain joined clients that have access to a local Domain Controller. If they don’t have access to a local Domain Controller the regular PTA process as shown in the beginning of this blogpost (and previous blogpost) is followed.

Note. For the client to automatically pass the credentials, the Azure AD endpoints must be in the intranet zone

image

Tip. Use GPO to change this for all clients in your network.

If you use your browser and navigate to Exchange Online you will still be prompted to enter your username (or select a username when used previously) but you are not required to enter your password:

image

If you use a domain hint in your URL like https://outlook.office.com/owa/inframan.nl, then the account is automatically logged on. One small but strange note, this is supported by Microsoft Internet Explorer, but not by the Microsoft Edge browser (at least not at the moment of writing, early November 2017). This might change in the future though.

To get this working with Outlook 2016 (or fully patched Outlook 2013 that supports Modern Authentication) we need to enable OAuth on a tenant level. To achieve this, logon use Remote PowerShell in Exchange Online using the following commands:

$Cred= Get-Credential 'administrator@contoso.onmicrosoft.com'
$Session= New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/PowerShell-LiveID -Credential $Cred -Authentication Basic -AllowRedirection
Import-PSSession -Session $Session

And when logged in enter the following command:

Set-OrganizationConfig -OAuth2ClientProfileEnabled:$TRUE

image

Next time you start Outlook you will see that it will automatically logon to Exchange Online (whereas it didn’t when Oauth was not enabled).

Note. As outlined earlier in this post there’s a shared key between the computer account in your on-premises Active Directory and Azure Active Directory. It is strongly recommended to roll-over these keys every 30 days. For more information check the Microsoft FAQ on this: https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnect-sso-faq

Summary

You can use Pass-through authentication if you have a requirement to keep all user passwords on-premises (and thus not store them in the Microsoft cloud). When using Pass-through authentication you can also enable seamless Single-Sign On or sSSO. This way domain joined clients (that have access to a Domain Controller) can use Kerberos authentication to access services in the Microsoft cloud.

A number of issues to be aware of: not all clients do support PTA or sSSO as outlined in this article. For example, Internet Explorer does support it, but the Edge browser doesn’t. Outlook 2013/2016 do support it (modern authentication) but Outlook 2010 does not. Also, the Lync/Skype for business clients do not support this at all. I expect this to change in the (near) future, and when it does I will update this article.

More information

Azure Active Directory Seamless Single Sign-On: Frequently asked questions – https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnect-sso-faq

Cloud identities, Linked Identities and Federated Identities

When you are using a cloud service, whether it be Office 365, Facebook, LinkedIn or Gmail you are using a user account, and these are also referred to as ‘identities’. Typically there are three types of identities in a cloud service: Cloud Identities, Synced Identities and Federated Identities.

  • Cloud Identity – a Cloud Identity is a user account that’s created and managed in the cloud service. In case of Office 365 this account is created and managed in the Microsoft Online Portal. Important to note is that when you access an Office 365 service, authentication takes place against the Windows Azure Active Directory Domain Controllers.
    In the Microsoft Online Portal these accounts are easily identifiable as Cloud Identities as can be seen in the following figure:
    image
  • Synced Identity – a Synced Identity is created and managed in your local Active Directory and synchronized with the Cloud service. In Office 365 you can opt to synchronize the passwords as well, although not the actual password is synchronized but a hash of the password. Like Cloud Identities authentication takes place against the Windows Azure Active Directory Domain Controllers. These accounts are identified in the Microsoft Online Portal as ‘Synced with Active Directory’ as shown in the following figure:
    image
    Although the username and password are identical in Office 365 and in the local Active Directory, this is not a Single Sign-On solution, but I always refer to this as a ‘Same Set of Credentials’ solution.
  • Federated Identity – a Federated Identity is a user account that’s created and managed in your local Active Directory and that’s synchronized with Office 365. When the account is synchronized an account in Office 365 (Windows Azure Active Directory) is created. When a service in Office 365 is accessed, the user is not authenticated against the Windows Azure Active Directory Domain Controllers, but the authentication request is redirected to your local Active Directory and Domain Controllers. To achieve this an Active Directory Federation Service (ADFS) needs to be in place. Since there’s only one set of credentials (all authentication takes place against your local Domain Controllers!) this is referred to as ‘Single Sign-On’.

Continue reading Cloud identities, Linked Identities and Federated Identities