[iOS] AppAuth crash when user clears Safari history mid-session

[willperkins]

Describe the bug
App crashes if clearing Safari history while in an authentication session.

To Reproduce
Steps to reproduce the behavior:

1. Start a OIDExternalUserAgentSession, using for example: OIDAuthState.authState(...)
2. Switch to iOS Safari Settings, clear history and website data — closing all tabs
3. Return to app
4. Hit cancel on the alert that displays
5. App will crash

Expected behavior
Alert dismisses

Environment

• Device: iOS simulator, iOS devices
• OS: iOS13+
• Browser: Safari

Additional context
It looks like this is a known issue in ASWebAuthenticationSession. See radr: https://openradar.appspot.com/FB12132525

A potential mitigation is to "retain the authentication session until after the dismiss animation is complete".

[git-wuweiyi3]

same here