I am developing one application where website users can send automated / transactional emails form their Gmail account. I am using socialite(Google) for website signup. How can I get user SMTP credentials without asking them.(maybe through oauth or something). As I know SMTP contain user email and user password. For security and privacy purpose I don't want to use or save that data in my application. My only goal here is too allow users sends email from their Gmail accounts.If some how I have to save users SMTP credentials what are the most secured way to do this?