exim auth database and system

i have got exim compiled with postgresql on debian;
in exim.conf:

auth_plain:
driver = plaintext
public_name = PLAIN
server_condition = ${lookup pgsql{SELECT user_idnr FROM users \
WHERE userid = '${quote_pgsql:$2}' AND passwd = '${quote_pgsql:$3}'}}
server_set_id = $2

auth_login:
driver = plaintext
public_name = LOGIN
server_condition = ${lookup pgsql{SELECT user_idnr FROM users \
WHERE userid = '${quote_pgsql:$1}' AND passwd = '${quote_pgsql:$2}'}}
server_prompts = "Username:: : Password::"
server_set_id = $1

auth_cram_md5:
driver = cram_md5
public_name = CRAM-MD5
server_secret = ${lookup pgsql{SELECT passwd FROM users \
WHERE userid = '${quote_pgsql:$1}'}{$value}fail}
server_set_id = $1

i am wondering how should i connect (what should i add) to server_condition
to check also usernames and password that are in system
(for ex how to add this: this server_condition = "${if pam{$2:$3}{1}{0}}") ???

SaPeR

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