Shared Accounts (POS/Kiosk) and Single Sign-On in the Same Environment

BACKGROUND

You have successfully configured Single Sign-on in Office 365 with the following conditions:

  1. ADFS is deployed with one internal pair (STS) and one external pair (Proxy), both pairs are load balanced. ADFS is running at least version 2.0 with the latest Update Rollup installed.
  2. Clients that resides on the internal network have the ADFS URL (in this example sts.Company.com) pointing to the ADFS STS server pair (the LB VIP).
  3. Clients that resides on the external network have the ADFS URL (sts.Company.com) pointing to the ADFS Proxy pair (the LB VIP).
  4. On all Active Directory-domain joined clients, the ADFS URL (sts.Company.com) is added to the Local Intranet Zone using a Site-to-Zone Assignment List GPO.
  5. You have not configured ADFS to allow Single Sign-on for non-IE browsers (Disable Extended Protection).
  6. You have verified that Single Sign-on works as expected by navigating to http://outlook.com/OWA/company.com (where Company.com is a custom domain that is configured as a Federated Domain in your Office 365 tenant). When navigating to the URL, you are redirected to Outlook Web App without being prompted for credentials.

This scenario is exactly what we want for our users that are logging on to Windows everyday using their personal Active Directory account. It is a seamless solution that allow the user to consume Office 365 services without entering credentials multiple times through-out the working day.

The problem is if parts of the organization is using common/shared Active Directory accounts for logging on to Windows. A few examples of when common Active Directory accounts are used for logging on to Windows are at: Point of Sale terminals (POS), front desk/receptions, and at heavy industry operation sites (factory users are restricted by gloves/outfit).

These users will not be able to access their personal Office 365 services as they are logged in to Windows with the shared account, and when attempting to access, for example, Outlook Web App, they either get a message that the current account does not have a valid license (if the shared account is not licensed), or they will be logged in to the wrong mailbox (if a licensed user is logged on to Windows when the other user is taking over the session). The user have no chance to login as themselves to reach their personal mailbox etc, as we have configured Single Sign-on to Office 365, without any credential prompts allowed.

In summary, we have a situation where users logging on with personal Active Director accounts to their personal computers have a perfect experience with Single Sign-on, but our users without personal computes that are logging on to Windows with shared accounts, are simply not able to reach their mailbox and other data without first logging in to Windows with their personal account – which is not feasible for the business operation.

CAUSE

This bevaviour is fully expected. It is not ideal for users to share Active Directory accounts for loggin on to Windows, both from the security perspective (complicance and auditing) and from the functional perspective (single sign-on and personal data access). To remediate it, the general recommendation is of course to have all users logging on to Windows with personal Active Directory accounts, but in reality, this is not always possible. The reasons are many, and they are not described on TechNet or in any text book examples, but they are usually related to the time it actually takes to log off and log back on. At a POS, every lost second can be a lost sale, and at the factory floor, every lost second can be a compromise of a persons safety.

Technically, our Single Sign-on configuration is doing exactly what it is supposed to do. A user attempts to reach Outlook Web App, get’s redirected to ADFS STS and authenticates using the Kerberos TGT-ticket issued for the shared account when logging on to Windows. ADFS grants a Token, including claims for the shared account. The Token is then presented to Office 365, who translates the claims to either a non-licensed user (giving the No license error), or if it exist, to the mailbox for the shared account (loading the wrong mailbox for the user).

RESOLUTION

To remediate this problem, without affecting the Single Sign-on experience for our Office workers with personal computers, we must break the Single Sign-on configuration only for the shared accounts.

To accomplish this, we will configure the Site to Zone Assignment List GPO.

As stated in the Background above, the ADFS URL sts.Company.com is added to the Local Intranet Zone to allow Single Sign-on. If we remove it from there, the user will not be able to present the Kerberos TGT-ticket when logging on, and we will prompted for credentials again. This is a bad user experience and should never be the routine for Office users with personal computer and personal accounts, but such credential prompt is what can allow a user that has logged on with a shared user account to actually login to Outlook Web App (or other Office 365 Service) with a personal account and reach the personal mailbox.

High-level description of the solution:

  1. Depending on how Group Policy is used in your organization today, first decide if this setting should be computer based or user based. Both can be applied for this.
  2. Configure separate Site to Zone Assignment List GPO’s for personal Active Directory accounts and for common/shared Active Directory accounts. (Or for personal computers or shared computers, depending of outcome in #1).
  3. For the personal account/computer GPO, place sts.Company.com in the Local Intranet Zone – this will give them Single Sign-on
  4. For the shared accounts/computers, Place sts.Company.com in the Trusted Sites zone – this will break Single Sign-on and give the user a credential prompt on access to the services. The user can respond to the credential prompt with personal credentials and by that accessing the personal mailbox/data.

Here is a good overview of the Site to Zone Assignment List GPO: http://blogs.msdn.com/b/askie/archive/2012/06/05/how-to-configure-internet-explorer-security-zone-sites-using-group-polices.aspx (Scroll down a bit).

COMMENT: Some organizations solves this issue by letting all clients redirect sts.company.com to the ADFS Proxy even internally. This methdo will also present the credential prompt, but it will affect all users – including those that are using personal accounts on personal computers – which is a bad user experience for them. Using GPO and Site to Zone assignment is  a better way to go.