> For the complete documentation index, see [llms.txt](https://docs.lithnet.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lithnet.io/ams/help-and-support/support-articles/kb000012.md). # KB000012: Troubleshooting Windows authentication in the Access Manager Web App ## Summary Incorrect configuration of Windows authentication can cause users to be trapped in an authentication loop. This prevents them from accessing the web application. ## Cause There are several possible causes for Windows authentication not working. ### 1. Incorrect SPN The hostname that the user types into their address bar must be registered as an SPN on the service account in Active Directory. The SPN must be in the format of `HTTP/hostname` where `hostname` is the fully qualified host name that the user is entering into their browser. ``` You can use the `setspn` command to manage SPNs. - View a list of SPNs assigned to a service account `setspn -L domain\serviceaccount` - View which account an SPN is assigned to `setspn -Q HTTP/hostname` - Set the SPN on a service account `setspn -S HTTP/hostname domain\serviceaccount` ``` ### 2. Mismatched encryption types Ensure that AES encryption types are enabled for the AMS service account. If you have performed hardening and disabled RC4, enabling AES may be required to ensure that a compatible encryption type can be negotiated. ![](https://3858442128-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fq1NRJ1mSUxsI5xgqtLGt%2Fuploads%2Fgit-blob-df52c7d23de9d8d6a9a0fa53ad8b18654ea8313c%2Fkrb-aes-options.png?alt=media) ### 3. Use of CNAME records Chrome-based browsers have a behavior where they [try to authenticate as the target of the CNAME record](https://www.chromium.org/developers/design-documents/http-authentication/). If the user types `https://ams.lithnet.io` in their address bar, Chrome checks to see if `ams.lithnet.io` is a CNAME. If it is, rather than requesting a Kerberos ticket for `HTTP/ams.lithnet.io`, it requests it for the underlying A record target instead. This is typically the machine itself, e.g., `HTTP/AMS1.domain.local`. The AMS service performs authentication as the service account, rather than the machine account. As a result, mutual authentication fails. Possible solutions for this * Convert the `ams.lithnet.io` record to an A record * Use Chrome policy to [disable this behavior](https://chromeenterprise.google/policies/#DisableAuthNegotiateCnameLookup). However, be aware this will impact all sites using Windows authentication. It should be tested carefully to ensure it doesn't impact other services. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.lithnet.io/ams/help-and-support/support-articles/kb000012.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.