Migrating DHCP configuration from v3 to v4

[Ľudovít Mikula]

I am migrating my dhcp setup from freeradius v3 into v4 and have some 
questions.

In v3 there was a dedicated dhcp and dhcp-ippool mods-config/sql setup, 
where the sql_user_name was set to:
     sql_user_name = "%{control:DHCP-SQL-Option-Identifier}"
and in my processing sections I have set the 
"control:DHCP-SQL-Option-Identifier" based on some custom logic.

In v4 there is no such configuration, but the comments in ippool queries 
seem to suggest it can now all be done in one config.

However when using ippool module in DHCP request processing, the 
%{User-Name} attribute (configured in sql_user_name) is not known and I 
have not found an alternative to DHCP-SQL-Option-Identifier attribute.

What is the recommended way of migrating such configuration from v3 into v4?

Thank you.

-- 
Ludo Mikula