override func viewDidAppear(_ animated: Bool) {
        let keychain = Keychain(service: "kfurue.RxSwiftRailsTutorial-token")

        if keychain["oauthToken"] == nil {
            oauthswift.authorizeURLHandler = SafariURLHandler(viewController: self, oauthSwift: oauthswift)
            oauthswift.authorize(
                withCallbackURL: URL(string: "sample-app://oauth-callback")!,
                scope: "", state: "hoge",
                success: { credential, _, _ in
                    print(credential.oauthToken)
                    // OAuthSwiftで取得したトークンをKeychainにストアする
                    keychain["oauthToken"] = credential.oauthToken
            },
                failure: { error in
                    print(error.localizedDescription)
            }
            )
        }

    }