[flutterfire_ui] add support for email link sign in on web

[lesnitsky]

Any plans to expand email link sign-in to web (currently only iOS and Android)?

Originally posted by @wolframm in https://github.com/FirebaseExtended/flutterfire/discussions/6978#discussioncomment-1804939

[jbryanh]

Excited to see this getting close to fruition. Have an app that does not use passwords, and I need to create a web app, so this would be nice. I assume it means that dynamic_links is close to being available for web. How soon? Happy to help test or whatever.

[lesnitsky]

I think the way this could be handled is via flutter's routing mechanism. This would only work on a hosted flutter web app.

Example scenario:

• you have your app deployed to the https://myawesome.web.app
• email link provider is configured to send a link that directs the user to the https://myawesome.web.app/email-link-sign-in?<sign-in-link-payload-goes-here>
• flutterfire_ui exports onGenerateRoute (or routeInformationParser and routerDelegate for WidgetsApp.router) that handles /email-link-sign-in route, gets the payload and sends it down to the underlying firebase SDK

Adding these to the flutterfire_ui directly would require less effort, rather than making dynamic_links work on the web, but the latter is also doable (at least in my head)

[ywake]

I hope for web support.

By the way, to support web, two things are necessary: the redirect URL inside DynamicLink and the entered email address. The URL can be obtained with GoRouter or similar, and for retrieving the entered email address, I've added a callback to EmailLinkSignInScreen.

I consider this a temporary solution, so I haven't created a pull request for it, but please refer to it if you're looking for a simple implementation.

https://github.com/ywake/FirebaseUI-Flutter/tree/email-link-web diff

More details are in Japanese here.