OIDC redirect sometimes fails to be picked up.

[pixlwave]

Steps to reproduce

1. Sign out of the app
2. Choose a homeserver with OIDC configured
3. Try to sign in to the app.

Outcome

What did you expect?

Sign in would complete.

What happened instead?

Sign in almost finishes, but instead of the redirect being picked up by the app, the ASWebAuthenticationSession navigates to the page (which doesn't exists so it 404s).

How to fix

• Initially lets revert back to using io.element:/callback as the redirect URL, as the WAS handles the redirection itself and we know it works reliably. (done ✅)
• As we would really like to use the universal link, we should host a fallback HTML page on http://mobile.element.io/ which opens up the app with the custom URI scheme. This will need additional parsing added to the URL routes on the app side.

Your phone model

N/A

Operating system version

iOS 17

Application version

1.3.4

Homeserver

No response

Will you send logs?

No

[pixlwave]

Adding a note that iOS 17.4 deprecated the ASWebAuthenticationSession init with a scheme, replacing it with a URL: https://developer.apple.com/documentation/authenticationservices/aswebauthenticationsession/init(url:callback:completionhandler:)-6nut7

We should try this again as it sounds like we won't need the fallback page and can simply use the scheme on older devices and the URL on newer ones.