Reactive extension for "Sign in with Apple"

AppleSignIn+Rx.swift

import AuthenticationServices
import RxCocoa
import RxSwift

@available(iOS 13.0, *)
private class RxAppleSignInDelegateProxy: DelegateProxy<ASAuthorizationController, ASAuthorizationControllerDelegate> {

    private(set) var controller: ASAuthorizationController?
    fileprivate var signInSubject = PublishSubject<ASAuthorization>()

    init(controller: ASAuthorizationController) {
        self.controller = controller
        super.init(parentObject: controller, delegateProxy: RxAppleSignInDelegateProxy.self)
    }

    deinit {
        signInSubject.onCompleted()
    }
}

// MARK: - DelegateProxyType
@available(iOS 13.0, *)
extension RxAppleSignInDelegateProxy: DelegateProxyType {
    static func registerKnownImplementations() {
        self.register(make: RxAppleSignInDelegateProxy.init)
    }

    class func currentDelegate(for object: ASAuthorizationController) -> ASAuthorizationControllerDelegate? {
        return object.delegate
    }

    class func setCurrentDelegate(_ delegate: ASAuthorizationControllerDelegate?, to object: ASAuthorizationController) {
        object.delegate = delegate
    }
}

// MARK: - ASAuthorizationControllerDelegate
@available(iOS 13.0, *)
extension RxAppleSignInDelegateProxy: ASAuthorizationControllerDelegate {

    func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
        signInSubject.onNext(authorization)
        signInSubject.onCompleted()
    }

    func authorizationController(controller: ASAuthorizationController, didCompleteWithError error: Error) {
        if (error as NSError).code == ASAuthorizationError.canceled.rawValue {
            signInSubject.onCompleted()
            return
        }
        signInSubject.onError(error)
    }
}

// MARK: - Reactive
@available(iOS 13.0, *)
extension Reactive where Base: ASAuthorizationController {

    func signIn() -> Maybe<ASAuthorization> {
        let proxy = appleSignInDelegate
        proxy.signInSubject = PublishSubject<ASAuthorization>()
        return proxy.signInSubject
            .asObservable()
            .do(onSubscribed: { in
                proxy.controller?.performRequests()
            })
            .take(1)
            .asMaybe()
    }

    private var appleSignInDelegate: RxAppleSignInDelegateProxy { RxAppleSignInDelegateProxy.proxy(for: base) }
}