Documentation

Login: Link auto login

This explains how to immediately redirect a user into Platform after he’s signed in in a portal

varbackendUrl = "http://testing.sinesy.it/platformpicktour/"
backendUrl += "/4ws/index_app.jsp?autoLogin=true&applicationId=
PICKTOUR&appTitle=PickTOUR&companyId=00000&siteId=100";
backendUrl += "&username=" + encodeURIComponent(userId); backendUrl += "&password=" + encodeURIComponent(password); backendUrl += "&languageId=en&theme4ws=false&loginVersion=1&isIE=true"; backendUrl += "&hiddenItemIds=companyId=00000,siteId=100";

You just have to replace the red characters with the user data.
NOTE:  To allow the user change its password you can follow this guide.
For more info: PickTOUR – Luca Biasotto