When you click the sign up/in button on the homepage, open an overlay (blur the background) with:
A sign up and sign in option, with a button to swap between the two
Sign up should have email/password option or Google option
If successfully signed in (or signed up with google), close the overlay
If successfully signed up with email, notify them to check their email to verify their account. And have a option beside it to sign in once they've verified
Display any errors: missing email/password, invalid/too short email/password wrong email/password, email not verified (if anything else fails, just give a 'An error occurred, please try again later' message)
When you click the sign up/in button on the homepage, open an overlay (blur the background) with: