you must configure the authentication in both now so that it works, you need to create an acl of groups with AD in the squidguard by changing the parameters of the example:
ldapusersearch ldap://192.168.0.100/DC=domain,DC=com?sAMAccountName?sub?(&(sAMAccountName=%s)(memberOf=CN=it%2cCN=Users%2cDC=domain%2cDC=com))