I want to use my personal google account to send emails from the app and to upload documents to my google drive. I have everything set up in flutter, my only issue is authorization.

For more context: My app should have around 2-10 users. The user will fill some forms on my app, which will be exported as PDFs. I want to upload these PDFs to my personal GDrive and send them to a specific email from my personal email. To achieve this my credentials should somehow be saved on the app without expiration or risk of hacking. Is there a way to achieve this? or an alternative to this method?

OAuth2 the bane of my existence.