So the solution here is for a developer to add a bunch of code to their codebase on at least 4 platforms just to get to the same exact functionality and level of privacy, but with a worse user experience?
> For the third, don’t make me type in someone’s email. The exact same issue as described happens if they have multiple email addresses too. Just let me use my OS’s sharing mechanism to send a special link that they can open to establish the sharing connection. An invite to share, as it were. Not only does that solve the problem, it’s significantly more user-friendly.
As a user, I find that functionality to be incredibly clunky by comparison (on all platforms). It may be moderately better on iOS than Android, but even then Anylist and others are running multiplatform apps. If I'm using a computer and I need to manually copy a link, open my email client, compose a new email, type the subject and a message, paste the link, and hit send, that feels dramatically more cumbersome than just entering an email address and hitting "share". It also takes a good amount of new code to implement something like that on an existing system that uses email-based sharing, which I don't think developers should have to deal with just because Apple built a lousy login system.
You need to support letting the user change their email address anyway. Letting them change it from the privacy forwarding email to something else is no different. And that shouldn’t even interfere with using Sign In With Apple going forward because surely you’re using the user’s unique identifier from Apple to associate the sign-in with your service’s user.
Also FWIW you can use the Sign In With Apple JS approach on non-Apple platforms. This is obviously useful for web, but Apple’s developer site says it’s “for web and apps on other platforms” so you could use this from Android too, it will just take some more work.
> As a user, I find that functionality to be incredibly clunky by comparison (on all platforms).
As a user, I have never connected with someone on a service by typing in their email address. Not only do people routinely have multiple email addresses (e.g. work and personal), but people also often use unique addresses for services (e.g. plus addresses), so it’s not at all a reliable mechanism.
> If I'm using a computer and I need to manually copy a link, open my email client, compose a new email, type the subject and a message, paste the link, and hit send
Why would you do all this? The service can offer a mailto: link that pre-fills the body, so all you have to do is click it, type in the recipient’s email address, and hit Send. And this lets you customize the message as appropriate. Better yet, on Apple platforms you can use the built-in share functionality, including on web with the Web Share API.
And if you really don’t want to do all of that, you could have me enter an email that you send a special link to rather than looking up in your user database. That’s still not great for me as a user because it means I’m giving you someone else’s email address, which I don’t want to do, but it’s better than nothing.
The simple fact is, if your sharing mechanism requires me to know the email address someone else has already used to sign up for your service, it’s a crappy sharing mechanism.