Deeplink query parameters user details validation improvement

[kariot]

Added validation to the user object received via the deep link. It already checks for the presence of the user object, but it could still be empty in sign-in scenarios and interrupt the sign-in flow due to JSON decode error.

[tp]

@kariot Sorry, for the initial response. I got this mixed up and read it as a bug report and not a PR…

Where you able to capture the incoming deep link to show how it's not matching expectations?

Was it really contains user= instead of no user parameter at all? Just surprised, because
per the documentation at https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_js/incorporating_sign_in_with_apple_into_other_platforms I would always expect it in a non-error case:

But maybe there is a case, e.g. when not requesting any scopes, when it will be absent?

[kariot]

Hi @tp,

I've noticed the issue where I was receiving an empty user object—meaning the user key is present, but it has no associated value. I was able to reproduce this by signing up from an iOS device and then signing in from an Android device, which seems to cause a crash.