[iOS] Social login

[nadonomy]

Goal: Implement matrix-org/matrix-spec-proposals#2858

Related issues:

• Android: [Android] Social login element-android#2452
• Web: Social Login and login delight tweaks matrix-org/matrix-react-sdk#5426
• Spec: MSC2858: Multiple SSO Identity Providers matrix-org/matrix-spec-proposals#2858

Design:

[kensington]

Handle redirect on SSO Web page: Implement a new WKWebView or use
SFSafariViewController. See https://matrix.org/docs/spec/client_server/r0.6.1#sso-client-login.

+1 for SFSafariViewController - this is required to support WebAuthn properly. Without it, fallback to eg. TOTP doesn't even necessarily work as the IDP can't necessarily detect the lack of WebAuthn support and waits for a response that cannot come.

[SBiOSoftWhare]

TODO:

• Handle new login flow m.login.sso format in SDK (see https://github.com/matrix-org/matrix-doc/blob/t3chguy/msc/multi-sso/proposals/2858-Multiple-SSO-Identity-Providers.md#proposal)
• Make social login provider list and buttons
• Handle SSO providers on register screen
• Handle SSO providers on login screen
• On login/register screen: refresh SSO providers on custom HS change
• Handle redirect on SSO Web page. See https://matrix.org/docs/spec/client_server/r0.6.1#sso-client-login.
  • Use SFAuthenticationSession for iOS 11
  • Use ASWebAuthenticationSession for iOS 12+
  • Use SFSafariViewController as fallback only when VoiceOver is enabled (https://openradar.appspot.com/48376122)
• Test all SSO providers on a test HS

[richvdh]

@SBiOSoftWhare @nadonomy can this be closed?