How To Enable Authentication For LDAP Users

You can setup Kerberos SSO or you can enable basic authentication for LDAP user 

Access the SafeSquid User Interface 

File:SafeSquid Interface.jpg

Go to configure page on top right corner of the interface

Then on left side go to Application Setup ==> Access Restrictions 

you will see that the in Global section  by default SSO is enabled

Make SSO disable 

Then Move to the Allow list subsection and create the policy same as below

Read more about  Authentication with kerberos SSO