Update Slack provider to use v2 API and allow Bot tokens (#645)

* Update Slack driver to use v2 API and allow Bot tokens

* Update SlackProvider.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/Two/SlackProvider.php

@@ -14,20 +14,39 @@ class SlackProvider extends AbstractProvider
      */
     protected $scopes = ['identity.basic', 'identity.email', 'identity.team', 'identity.avatar'];
 
+    /**
+     * The key used for scopes.
+     *
+     * @var string
+     */
+    protected $scopeKey = 'user_scope';
+
+    /**
+     * Indicate that the requested token should be for a bot user.
+     *
+     * @return $this
+     */
+    public function asBotUser()
+    {
+        $this->scopeKey = 'scope';
+
+        return $this;
+    }
+
     /**
      * {@inheritdoc}
      */
     public function getAuthUrl($state)
     {
-        return $this->buildAuthUrlFromBase('https://slack.com/oauth/authorize', $state);
+        return $this->buildAuthUrlFromBase('https://slack.com/oauth/v2/authorize', $state);
     }
 
     /**
      * {@inheritdoc}
      */
     protected function getTokenUrl()
     {
-        return 'https://slack.com/api/oauth.access';
+        return 'https://slack.com/api/oauth.v2.access';
     }
 
     /**
@@ -55,4 +74,38 @@ protected function mapUserToObject(array $user)
             'organization_id' => Arr::get($user, 'team.id'),
         ]);
     }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function getCodeFields($state = null)
+    {
+        $fields = parent::getCodeFields($state);
+
+        if ($this->scopeKey === 'user_scope') {
+            $fields['scope'] = '';
+            $fields['user_scope'] = $this->formatScopes($this->scopes, $this->scopeSeparator);
+        }
+
+        return $fields;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getAccessTokenResponse($code)
+    {
+        $response = $this->getHttpClient()->post($this->getTokenUrl(), [
+            RequestOptions::HEADERS => $this->getTokenHeaders($code),
+            RequestOptions::FORM_PARAMS => $this->getTokenFields($code),
+        ]);
+
+        $result = json_decode($response->getBody(), true);
+
+        if ($this->scopeKey === 'user_scope') {
+            return $result['authed_user'];
+        }
+
+        return $result;
+    }
 }