Troubleshooting CAS

Changes Coming Soon

We will be retiring support for CAS in June of 2021. To utilize SSO to login into the Formstack platform after this date, please configure your identification provider for SAML 2.0. This does not apply to External Form Authentication, where CAS, LDAP, and Active Directory will remain active.

The CAS (Central Authentication Service) requires your server to have a properly configured Hostname, Port, and Context.  For new configurations or adjustments to existing configurations, we recommend having your IT department pre-configure these settings and certificates before engaging with the Formstack setup.


Common Errors & Recommended Troubleshooting 


Error: “Username already exists for this authentication provider”

This usually means an existing account has another authentication method enabled. If so, the user should sign in using that method (such as email and password).

This error message can also be received if the Username Attribute of their CAS credentials doesn’t match the username of their account. If so, the user can update the attribute at their identity provider (for instance, back to the old value if it had been previously updated).  


Error: "ERROR: Authentication failed due to invalid response from the Central Authentication Service (CAS) server."


This can occur when the CAS Auth Provider has been setup incorrectly, specifically the “CAS Context” field being empty or set to the wrong input. As a fix, we recommend using “/cas” as the input to see if this resolves the error. 

Additionally, you will want to confirm what this should be set to. Normally, if you navigate to “” > Login > “/cas” is supposed to be the context.



Error: The option to add an External Username does not appear on all accounts


You will need to have a CAS Authentication Provider added.


Error: ERROR: Unable to look up username because AuthProvider Id to use is not valid


Our system may be unable to read the username from the response in CAS. Confirm you are sending over the “username” or “uid” property on the user response. Beyond that, we would also recommend removing and re-adding the SSO configuration in your Formstack account.  If the issue persists, please contact Formstack Support. 


Error: ERROR: Invalid Authentication Provider Action


This generally indicates that the URL was entered incorrectly; either an invalid URL or a URL on a different account. This error may also occur if the URL was deleted and recreated by the Auth Provider. We recommend first verifying your URL with your Auth Provider and then remove and manually re-enter under the SSO configuration in your Formstack account.

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