asterisk users - Dec 2004 - H.323 link to provider VoIP with Username and Pass

Hi,

- I have account on VoIP provider sample.net with auth for example 
Username: test and Password: test

- this provider VoIP use only H.323 and I must use softphone with H.323 
support to make phone to PSTN via this provider

My idea is configure asterisk to possible make phone from my users SIP 
softphones to PSTN via this provider sample.net.

- I have asterisk with support H.323 ( Ihave use 
http://www.inaccessnetworks.com/projects/asterisk-oh323)
- I have OpenH323 GateKeeper GnuGK if it is necessary
- in my extension.conf I have:

exten => _3xxxxx,1,Dial(OH323/${EXTEN:1}@sample.net)

but now I have problem how to configure oh323.conf to make phone to PSTN 
via provider sample.net which to require auth Usernmae and PASS.
Maybe I must use GunGK with asterisk but I don't know Hot to configure 
to send username and Pass.

For SIP provider is simple definition in sip.conf but How to this make 
via H.323 ?

It is possible to configure asterisk for this?