Asterisk as Dial-IN Ras from sip-trunk

Hi all,
How can I use asterisk as Dial-IN RAS Server using PPP?

I have several modem and POS that connect to my SIP Trunk number , I want set asterisk to send IP address to pos/modem and permit them to login my network via sip trunk .

1- how can I do it ( I see the Asterisk cmd PPPD but It can work only with Serria ISDN , not for Sip trunk )
2- is it possible for asterisk to authenticate Dialin User using ppp protocol ?

It’s not possible for Asterisk to do this over SIP.