SFAuthenticationSession.CompletionHandler
The completion handler for an authentication session when the user cancels or finishes the login.
Declaration
typealias CompletionHandler = (URL?, (any Error)?) -> VoidDiscussion
The custom callback URL should only be a custom URL scheme, and not a standard scheme (e.g. http or https). The session looks at the scheme registered first and routes to the app asking to start a session before potentially routing the scheme to another app.