Sorry, you can't access Workfront thru this login screen. Workfront is setup for
Federated single sign-on with SAML 2.0. Please contact your system administrator.
The URL will show: https://yourdomain.my.workfront.com/login?ssoError=exception.sso.usernotmapped
The user's Federated ID does not match what is being passed into Workfront from SSO.
Edit the user and make sure their Federated ID matches what you're passing in from SSO to the user's $$NAMEID field (including Case Sensitivity)
If you're not sure what you've defined - go to Setup > System > Single Sign-On (SSO) > Edit Settings > Edit Configuration > click the "Test Connection" Button. The results screen will show you what attribute name and value you're passing into Workfront from SSO.