use login hint for second sign-in if we already know the user email

[tomholub]

It can be improved further: on the second sign-in attempt, supply login hint into the google sign-in request. That way, I don't have to choose my email again, instead my email will be pre-chosen based on the first sign-in.

Originally posted by @tomholub in #663 (comment)

[tomholub]

Also, when the user successfully proceeds, the user email that they logged in with has to be cross-checked against the user email that they logged in with the first time, to make sure that the user didn't explicitly select another account during login.

If the emails don't match, do not save any of the new login tokens, and show a modal that the just used account xxx differs from already signed in account yyy, and that they should use yyy to log in.

[tomholub]

Follow browser extension behavior. To understand this issue:

1. go to accounts.google.com on your account -> 3rd party apps -> flowcrypt ios -> revoke
2. login on ios app with that account, but don't tick Gmail permission during the grant screen
3. you will be prompted to login / grant again

current behavior: the user has to select their email account address again, especially if you are logged into more than one account

expected behavior: since user already signed in once (even though without granting permission), we should already know user email. The second login prompt should use that email address in a login_hint so that user doens't have to choose their email address again.

The very same thing applies when user then goes to compose screen and wants to grant contacts permission - login_hint should always be used there since user is already logged in.

[tomholub]

Thanks for thinking about this.

Couldn't they Cancel on top left? Which is a failed login, which we could interpret as "cancel whole login procedure". At which point they could choose another account?

[tomholub]

Ok, for now, let's only add login_hint on the contacts prompt. Let's leave this issue open though. I'd like to discuss the login flow again sometime later.