How to access the missing_scope Error Messages that gets returned

1: Here's an example of how you can drill down into this kind of error:

switch callError as CallError {
case .authError(let authError, let userMessage, let errorSummary, let requestId):
    switch authError {
    case .missingScope(let tokenScopeError):
        print("Missing scope error: \(tokenScopeError)")
        print("The required scope is: \(tokenScopeError.requiredScope)")
    default:
        print("other AuthError omitted for brevity of example")
    }
default:
    print("other CallError omitted for brevity of example")
}

2: No, there's just the authorization flow as documented here.