Google SmartLock in Sign-up flow

If a user tries to sign-up with an email address which is already associated with a WordPress account they are redirected to the sign-in flow. However, the Google SmartLock account chooser is not shown in this flow and the user needs to use magic-link login or enter their password manually.

There are several ways how to go about it:

1. Easiest solution: Show the Google SmartLock account chooser on the LoginPrologue screen right after the user opens the app - only if the user has WordPress credentials stored in Google SmartLock.

2. Show the Google SmartLock account chooser after the user gets redirected from the sign-up flow to the "Login with magic link/Enter your password" screen. The downside of this solution is that we might show the Google SmartLock account chooser even for other email address not just the one the user has just entered. Moreover, the flow can be a bit confusing.

3. Investigate if it's possible to check whether a certain email address (the one user entered in the sign-up flow) is associated with a WordPress account and the credentials are stored in Google SmartLock. If it'd be possible we could simply login the user without asking for their password. (I've really quickly checked the documentation and I believe there is not reliable solution for this)

4. Close this issue as it's not worth fixing.

If it were up to me I'd go with 1. The benefit of this solution is users would be able to sign-in faster with less clicks.
I realize some users open the app and they are not planning to sign into their existing account, but I feel like the chance a user has a WordPress password stored in Google's SmartLock and they are not planning to sign in are quite low. Moreover, even if it happens, they can just click on cancel. All the other users (users who were planning to sign in) would save several clicks and they would be able to sign-in in a few seconds after they opened the app.

@SylvesterWilmott @iamthomasbishop Wdyt?

Start by tracing the sign-up redirect to the LoginPrologue and the "Login with magic link/Enter your password" screen, then review Google SmartLock's account-chooser behavior and limitations. The issue needs a decided flow before implementation; done means the chosen sign-in path reliably presents SmartLock credentials without confusing users.