Important This article contains information that shows you how to help lower security settings or how to turn off security features on a computer. You can make these changes to work around a specific problem. Before you make these changes, we recommend that you evaluate the risks that are associated with implementing this workaround in your particular environment. If you implement this workaround, take any appropriate additional steps to help protect the computer.
A federated user is repeatedly prompted for credentials when the user tries to authenticate to the Active Directory Federation Services (AD FS) service endpoint during sign-in to a Microsoft cloud service such as Office 365, Microsoft Azure, or Microsoft Intune. When the user cancels, the user receives the following error message:
The symptom indicates an issue with Windows Integrated authentication with AD FS. This issue can occur if one or more of the following conditions are true:
An incorrect user name or password was used.
Internet Information Services (IIS) authentication settings are set up incorrectly in AD FS.
The service principal name (SPN) that's associated with the service account that's used to run the AD FS federation server farm is lost or corrupted.
Note This occurs only when AD FS is implemented as a federation server farm and not implemented in a stand-alone configuration.
One or more of the following are identified by Extended Protection for Authentication as a source of a man-in-the-middle attack:
Some third-party Internet browsers
The corporate network firewall, network load balancer, or other networking device is publishing the AD FS Federation Service to the Internet in such a way that IP payload data may potentially be rewritten. This possibly includes the following kinds of data:
Secure Sockets Layer (SSL) bridging
Stateful packet filtering
For more information, see the following Microsoft Knowledge Base article:
2510193 Supported scenarios for using AD FS to set up single sign-on in Office 365, Azure, or Intune
A monitoring or SSL decryption application is installed or is active on the client computer
Domain Name System (DNS) resolution of the AD FS service endpoint was performed through CNAME record lookup instead of through an A record lookup.
Windows Internet Explorer isn't configured to pass Windows Integrated authentication to the AD FS server.
Before you start troubleshooting
Check that the user name and password are not the cause of the issue.
Make sure that the correct user name is used and is in user principal name (UPN) format. For example, firstname.lastname@example.org.
Make sure that the correct password is used. To double-check that the correct password is used, you may have to reset the user password. For more information, see the following Microsoft TechNet article:
To check that Kerberos problems are causing the issue, temporarily bypass Kerberos authentication by enabling forms-based authentication on the AD FS federation server farm. To do this, follow these steps:
Step 1: Edit the web.config file on each server in the AD FS federation server farm
In Windows Explorer, locate the C:\inetpub\adfs\ls\ folder, and then make a backup copy of the web.config file.
Click Start, click All Programs, click Accessories, right-click Notepad, and then click Run as administrator.
On the File menu, click Open. In the File Name box, type C:\inetpub\adfs\ls\web.config, and then click Open.
In the web.config file, follow these steps:
Locate the line that contains <authentication mode=, and then change it to <authentication mode="Forms"/>.
Locate the section that begins with <localAuthenticationTypes>, and then change the section so that the <add name="Forms" entry is listed first, as follows:
At an elevated command prompt, restart IIS by using the iisreset command.
Step 2: Test AD FS functionality
On a client computer that's connected and authenticated to the on-premises AD DS environment, sign in to the cloud service portal.
Instead of a seamless authentication experience, a forms-based sign-in should be experienced. If sign-in is successful by using forms-based authentication, this confirms that a problem with Kerberos exists in the AD FS Federation Service.
Revert the configuration of each server in the AD FS federation server farm to the previous authentication settings before you follow the steps in the "Resolution" section. To revert the configuration of each server in the AD FS federation server farm, follow these steps:
In Windows Explorer, locate the C:\inetpub\adfs\ls\ folder, and then delete the web.config file.
Move the backup of the web.config file that you created in the "Step 1: Edit the web.config file on each server in the AD FS federation server farm" section to the C:\inetpub\adfs\ls\ folder.
At an elevated command prompt, restart IIS by using the iisreset command.
Check that the AD FS authentication behavior reverts to the original issue.
To resolve the Kerberos issue that limits AD FS authentication, use one or more of the following methods, as appropriate for the situation.
Resolution 1: Reset AD FS authentication settings to the default values
If AD FS IIS authentication settings are incorrect, or IIS authentication settings for AD FS Federation Services and Proxy Services don't match, one solution is to reset all IIS authentication settings to the default AD FS settings.
The default authentication settings are listed in the following table.
Default Web Site/adfs
Default Web Site/adfs/ls
Anonymous authentication Windows authentication
On each AD FS federation server and on each AD FS federation server proxy, use the information in the following Microsoft TechNet article to reset the AD FS IIS virtual applications to the default authentication settings:
871179 You receive an "HTTP Error 401.1 - Unauthorized: Access is denied due to invalid credentials" error message when you try to access a Web site that is part of an IIS 6.0 application pool
Resolution 2: Correct the AD FS federation server farm SPN
Note Try this resolution only when AD FS is implemented as a federation server farm. Do not try this resolution in an AD FS stand-alone configuration.
To resolve the issue if the SPN for the AD FS service is lost or corrupted on the AD FS service account, follow these steps on one server in the AD FS federation server farm:
Open the Services management snap-in. To do this, click Start, click All Programs, click Administrative Tools, and then click Services.
Double-click AD FS (2.0) Windows Service.
On the Log On tab, note the service account that's displayed in This Account.
Click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
Type SetSPN –f –q host/<AD FS service name>, and then press Enter.
Note In this command, <AD FS service name> represents the fully qualified domain name (FQDN) service name of the AD FS service endpoint. It does not represent the Windows host name of the AD FS server.
If more than one entry is returned for the command, and the result is associated with a user account other than the one that was noted in step 3, remove that association. To do this, run the following command:
SetSPN –d host/<AD FS service name><bad_username>
If more than one entry is returned for the command, and the SPN uses the same name as the computer name of the AD FS server in Windows, the federation endpoint name for AD FS is incorrect. AD FS has to be implemented again. The FQDN of the AD FS federation server farm must not be identical to the Windows host name of an existing server.
If the SPN does not already exist, run the following command:
SetSPN –a host/<AD FS service name><username of service account>
Note In this command, <username of service account> represents the user name that was noted in step 3.
After these steps are performed on all servers in the AD FS federation server farm, right-click AD FS (2.0) Windows Service in the Services management snap-in, and then click Restart.
Resolution 3: Resolve Extended Protection for Authentication concerns
To resolve the issue if Extended Protection for Authentication prevents successful authentication, use one of the following recommended methods:
Method 1: Use Windows Internet Explorer 8 (or a later version of the program) to sign in.
Method 2: Publish AD FS services to the Internet in such a way that SSL bridging, SSL offloading, or stateful packet filtering don't rewrite IP payload data. The best-practice recommendation for this purpose is to use an AD FS Proxy Server.
Method 3: Close or disable monitoring or SSL-decrypting applications.
If you can't use any of these methods, to work around this issue, Extended Protection for Authentication can be disabled for passive and active clients.
Workaround: Disable Extended Protection for Authentication
Warning We do not recommend that you use this procedure as a long-term solution. Disabling Extended Protection for Authentication weakens the AD FS service security profile by not detecting certain man-in-the-middle attacks on Integrated Windows Authentication endpoints.
Note When this workaround is applied for third-party application functionality, you should also uninstall hotfixes on the client operating system for Extended Protection for Authentication. For more information about the hotfixes, see the following Microsoft Knowledge Base article:
Resolution 4: Replace CNAME records with A records for AD FS
Use DNS management tools to replace each DNS Alias (CNAME) record that's used for the federation service with a DNS address (A) record. Also, check or consider corporate DNS settings when a split-brain DNS configuration is implemented. For more information about how to manage DNS records, go to the following Microsoft TechNet website:
Resolution 5: Set up Internet Explorer as an AD FS client for single sign-on (SSO)
For more information about how to set up Internet Explorer for AD FS access, see the following Microsoft Knowledge Base article:
2535227 A federated user is prompted unexpectedly to enter their work or school account credentials
To help protect a network, AD FS uses Extended Protection for Authentication. Extended Protection for Authentication can help prevent man-in-the-middle attacks in which an attacker intercepts a client's credentials and forwards them to a server. Protection against such attacks is made possible by using Channel Binding Works (CBT). CBT can be required, allowed, or not required by the server when communications are established with clients.
The ExtendedProtectionTokenCheck AD FS setting specifies the level of extended protection for authentication that's supported by the federation server. These are the available values for this setting:
Require: The server is fully hardened. Extended protection is enforced.
Allow: This is the default setting. The server is partly hardened. Extended protection is enforced for involved systems that are changed to support this feature.
None: The server is vulnerable. Extended protection isn't enforced.
The following tables describe how authentication operates for three operating systems and browsers, depending on the different Extended Protection options that are available on AD FS with IIS.
Note Windows client operating systems must have specific updates that are installed to effectively use Extended Protection features. By default, the features are enabled in AD FS. These updates are available from the following Microsoft Knowledge Base article:
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products