external request of data

dear all

I plane new application that post request to my cs-cart this posted data hase (user name and password)

I do the addon that can get the posted data and check if the username&password is valid or not and if valid the script have the user_id but i need to resend the user_id to application again i can't do this also i need to do all these steps without opining the storefront how can i do this ?

plz help