Dear sir,
I have read your requirement. I have following quires
1. when user use roundcube email accounts , they use through your site ?
2. Is it independent script where user login and use it without help of your site ?
3. do you want , when user login to their email account , they will stay login to your site also?
4. In which technology project was developed ?
5. Please send me link so that I can check and understand actual requirement.
Thanks & regards