To enable Kerberos Constrained Delegation (KCD)
Navigate to System Configuration > Services.
Under Web proxy service, click Configure.
The Web Proxy Service page displays.
Click the Web Application Profiles tab.
From the list of Web Proxy Services, select the web proxy service you want.
The Edit Web Application Profile page displays.
Select the check boxes for the options you want:
Enable fallback – The Enable fallback option should be checked only if the Enable Kerberos Constrained Delegation option is checked.
The Enable fallback option prompts the user to enter their credentials again if KCD has failed for some reason. If Enable fallback is unchecked and KCD has failed, an error page is displayed.
On Firefox, Enable fallback works only if both Negotiate and NTLM are enabled on the backend resource, in their respective order. Enable fallback does not work on Safari in this case. Safari displays a prompt to re-enter credentials, but it keeps failing. Enable fallback works only when NTLM is the only authentication provider on the backend, which is not a supported configuration for KCD.
Click Save.