func authenticate(userIdentity: String?, accessKey: String?, completion: @escaping (_ error:LoginError?) -> ()) {
        guard   let username = userIdentity, validate(email: username),
                let password = accessKey, validate(password: password) else {
            completion(LoginError.invalidCredentials)
            return
        }

        magineKit.authenticate(with: .email(URLCredential(user: username.trimWhiteSpace(), password: password, persistence: .permanent))) { session in
            guard let error = session.error as NSError? else {

                let user = User ()
                user.name = session.content?.currentUser?.profile?.name
                user.identifier = session.content?.currentUser?.identifier

                completion (nil)
                return
            }

            let authError = LoginError(with: error)
            completion(authError)
        }
    }