我使用 3 个资源解决了这个问题:

I was able to solve this using 3 resources:

1. Flutter Facebook 登录 (与 Firebase)在 2020 年文章
2. 使用 Twitter 登录 指南
3. Dart OAuth1 库

1. The Flutter Facebook Sign In (with Firebase) in 2020 article
2. The Log in with Twitter guide
3. The Dart OAuth1 library

最终，我能够完全删除 flutter_twitter 包，但仍然支持 Sign在推特上.

Ultimately, I was able to completely remove the flutter_twitter package, yet still support Sign in with Twitter.

类似于 Facebook 解决方案中概述的 CustomWebView，我创建了一个 TwitterLoginScreen 如下:

Similar to the CustomWebView outlined in the Facebook solution, I created a TwitterLoginScreen like:

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';
import 'package:oauth1/oauth1.dart';

/// Twitter Login Screen.
/// See [Log in with Twitter](https://developer.twitter.com/en/docs/basics/authentication/guides/log-in-with-twitter).
class TwitterLoginScreen extends StatefulWidget {
  final twitterPlatform = Platform(
    'https://api.twitter.com/oauth/request_token', // temporary credentials request
    'https://api.twitter.com/oauth/authorize', // resource owner authorization
    'https://api.twitter.com/oauth/access_token', // token credentials request
    SignatureMethods.hmacSha1, // signature method
  );

  final ClientCredentials clientCredentials;
  final String oauthCallbackHandler;

  TwitterLoginScreen({
    @required final String consumerKey,
    @required final String consumerSecret,
    @required this.oauthCallbackHandler,
  }) : clientCredentials = ClientCredentials(consumerKey, consumerSecret);

  @override
  _TwitterLoginScreenState createState() => _TwitterLoginScreenState();
}

class _TwitterLoginScreenState extends State<TwitterLoginScreen> {
  final flutterWebviewPlugin = FlutterWebviewPlugin();

  Authorization _oauth;

  @override
  void initState() {
    super.initState();

    // Initialize Twitter OAuth
    _oauth = Authorization(widget.clientCredentials, widget.twitterPlatform);

    flutterWebviewPlugin.onUrlChanged.listen((url) {
      // Look for Step 2 callback so that we can move to Step 3.
      if (url.startsWith(widget.oauthCallbackHandler)) {
        final queryParameters = Uri.parse(url).queryParameters;
        final oauthToken = queryParameters['oauth_token'];
        final oauthVerifier = queryParameters['oauth_verifier'];
        if (null != oauthToken && null != oauthVerifier) {
          _twitterLogInFinish(oauthToken, oauthVerifier);
        }
      }
    });

    _twitterLogInStart();
  }

  @override
  void dispose() {
    flutterWebviewPlugin.dispose();
    super.dispose();
  }

  Future<void> _twitterLogInStart() async {
    assert(null != _oauth);
    // Step 1 - Request Token
    final requestTokenResponse =
        await _oauth.requestTemporaryCredentials(widget.oauthCallbackHandler);
    // Step 2 - Redirect to Authorization Page
    final authorizationPage = _oauth.getResourceOwnerAuthorizationURI(
        requestTokenResponse.credentials.token);
    flutterWebviewPlugin.launch(authorizationPage);
  }

  Future<void> _twitterLogInFinish(
      String oauthToken, String oauthVerifier) async {
    // Step 3 - Request Access Token
    final tokenCredentialsResponse = await _oauth.requestTokenCredentials(
        Credentials(oauthToken, ''), oauthVerifier);

    final result = TwitterAuthProvider.getCredential(
      authToken: tokenCredentialsResponse.credentials.token,
      authTokenSecret: tokenCredentialsResponse.credentials.tokenSecret,
    );

    Navigator.pop(context, result);
  }

  @override
  Widget build(BuildContext context) {
    return WebviewScaffold(
      appBar: AppBar(title: Text("Twitter Login")),
      url: "https://twitter.com",
    );
  }
}

然后，可以将来自此屏幕的 AuthCredential 结果传递给 FirebaseAuth.signInWithCredential.

Then, the AuthCredential result from this screen can be passed to FirebaseAuth.signInWithCredential.