diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -151,7 +151,7 @@
     'rsrc/css/sprite-conpherence.css' => '3b4a0487',
     'rsrc/css/sprite-docs.css' => '5f65d0da',
     'rsrc/css/sprite-gradient.css' => '4bdb98a7',
-    'rsrc/css/sprite-login.css' => '878ee4d8',
+    'rsrc/css/sprite-login.css' => '3c811008',
     'rsrc/css/sprite-main-header.css' => '92720ee2',
     'rsrc/css/sprite-menu.css' => '28281e16',
     'rsrc/css/sprite-minicons.css' => 'df4f76fe',
@@ -816,7 +816,7 @@
     'sprite-conpherence-css' => '3b4a0487',
     'sprite-docs-css' => '5f65d0da',
     'sprite-gradient-css' => '4bdb98a7',
-    'sprite-login-css' => '878ee4d8',
+    'sprite-login-css' => '3c811008',
     'sprite-main-header-css' => '92720ee2',
     'sprite-menu-css' => '28281e16',
     'sprite-minicons-css' => 'df4f76fe',
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1279,6 +1279,7 @@
     'PhabricatorAuthProviderOAuth1' => 'applications/auth/provider/PhabricatorAuthProviderOAuth1.php',
     'PhabricatorAuthProviderOAuth1Bitbucket' => 'applications/auth/provider/PhabricatorAuthProviderOAuth1Bitbucket.php',
     'PhabricatorAuthProviderOAuth1JIRA' => 'applications/auth/provider/PhabricatorAuthProviderOAuth1JIRA.php',
+    'PhabricatorAuthProviderOAuth1MediaWiki' => 'applications/auth/provider/PhabricatorAuthProviderOAuth1MediaWiki.php',
     'PhabricatorAuthProviderOAuth1Twitter' => 'applications/auth/provider/PhabricatorAuthProviderOAuth1Twitter.php',
     'PhabricatorAuthProviderOAuth2' => 'applications/auth/provider/PhabricatorAuthProviderOAuth2.php',
     'PhabricatorAuthProviderOAuthAmazon' => 'applications/auth/provider/PhabricatorAuthProviderOAuthAmazon.php',
@@ -4076,6 +4077,7 @@
     'PhabricatorAuthProviderOAuth1' => 'PhabricatorAuthProviderOAuth',
     'PhabricatorAuthProviderOAuth1Bitbucket' => 'PhabricatorAuthProviderOAuth1',
     'PhabricatorAuthProviderOAuth1JIRA' => 'PhabricatorAuthProviderOAuth1',
+    'PhabricatorAuthProviderOAuth1MediaWiki' => 'PhabricatorAuthProviderOAuth1',
     'PhabricatorAuthProviderOAuth1Twitter' => 'PhabricatorAuthProviderOAuth1',
     'PhabricatorAuthProviderOAuth2' => 'PhabricatorAuthProviderOAuth',
     'PhabricatorAuthProviderOAuthAmazon' => 'PhabricatorAuthProviderOAuth2',
diff --git a/src/applications/auth/provider/PhabricatorAuthProviderOAuth1.php b/src/applications/auth/provider/PhabricatorAuthProviderOAuth1.php
--- a/src/applications/auth/provider/PhabricatorAuthProviderOAuth1.php
+++ b/src/applications/auth/provider/PhabricatorAuthProviderOAuth1.php
@@ -52,9 +52,11 @@
 
       $client_code = $this->getAuthCSRFCode($request);
 
-      $callback_uri = $adapter->getCallbackURI();
-      $callback_uri = $callback_uri.$client_code.'/';
-      $adapter->setCallbackURI($callback_uri);
+      if ($adapter->shouldAddCSRFTokenToCallbackURI()) {
+        $callback_uri = $adapter->getCallbackURI();
+        $callback_uri = $callback_uri.$client_code.'/';
+        $adapter->setCallbackURI($callback_uri);
+      }
 
       $uri = $adapter->getClientRedirectURI();
 
@@ -75,8 +77,9 @@
 
     // NOTE: You can get here via GET, this should probably be a bit more
     // user friendly.
-
-    $this->verifyAuthCSRFCode($request, $controller->getExtraURIData());
+    if ($adapter->shouldAddCSRFTokenToCallbackURI()) {
+      $this->verifyAuthCSRFCode($request, $controller->getExtraURIData());
+    }
 
     $token = $request->getStr('oauth_token');
     $verifier = $request->getStr('oauth_verifier');
diff --git a/src/applications/auth/provider/PhabricatorAuthProviderOAuth1MediaWiki.php b/src/applications/auth/provider/PhabricatorAuthProviderOAuth1MediaWiki.php
new file mode 100644
--- /dev/null
+++ b/src/applications/auth/provider/PhabricatorAuthProviderOAuth1MediaWiki.php
@@ -0,0 +1,212 @@
+<?php
+
+final class PhabricatorAuthProviderOAuth1MediaWiki
+  extends PhabricatorAuthProviderOAuth1 {
+
+  const PROPERTY_MEDIAWIKI_NAME = 'oauth1:mediawiki:name';
+  const PROPERTY_MEDIAWIKI_URI = 'oauth1:mediawiki:uri';
+  const PROPERTY_PRIVATE_KEY = 'oauth1:mediawiki:key:private';
+  const PROPERTY_PUBLIC_KEY = 'oauth1:mediawiki:key:public';
+
+  public function readFormValuesFromProvider() {
+    $config = $this->getProviderConfig();
+    return array(
+      self::PROPERTY_MEDIAWIKI_NAME =>
+        $this->getProviderDomain(),
+      self::PROPERTY_MEDIAWIKI_URI =>
+        $config->getProperty(self::PROPERTY_MEDIAWIKI_URI),
+      self::PROPERTY_CONSUMER_KEY =>
+        $config->getProperty(self::PROPERTY_CONSUMER_KEY),
+      self::PROPERTY_CONSUMER_SECRET =>
+        $config->getProperty(self::PROPERTY_CONSUMER_SECRET),
+    );
+  }
+
+  public function readFormValuesFromRequest(AphrontRequest $request) {
+    $is_setup = $this->isSetup();
+    if ($is_setup) {
+      $name = $request->getStr(self::PROPERTY_MEDIAWIKI_NAME);
+    } else {
+      $name = $this->getProviderDomain();
+    }
+
+    return array(
+      self::PROPERTY_MEDIAWIKI_NAME => $name,
+      self::PROPERTY_MEDIAWIKI_URI =>
+        $request->getStr(self::PROPERTY_MEDIAWIKI_URI),
+      self::PROPERTY_CONSUMER_KEY =>
+        $request->getStr(self::PROPERTY_CONSUMER_KEY),
+      self::PROPERTY_CONSUMER_SECRET =>
+        $request->getStr(self::PROPERTY_CONSUMER_SECRET),
+    );
+  }
+
+  public function getProviderName() {
+    return pht('MediaWiki');
+  }
+
+  protected function getProviderConfigurationHelp() {
+    $login_uri = PhabricatorEnv::getURI($this->getLoginURI());
+
+    return pht(
+      "To configure MediaWiki OAuth, create a new \"consumer\" here:".
+      "\n\n".
+      "https://www.mediawiki.org/wiki/".
+      "Special:OAuthConsumerRegistration/propose".
+      "\n\n".
+      "When creating your application, use these settings:".
+      "\n\n".
+      "  - **Callback URL:** Set this to: `%s`".
+      "\n\n".
+      "After you register the consumer, a **Consumer Key** and ".
+      "**Consumer Secret** will be provided to you by MediaWiki. ".
+      "To complete the configuration, copy the provided keys into ".
+      "the corresponding fields above.",
+      $login_uri);
+  }
+
+  protected function newOAuthAdapter() {
+    $config = $this->getProviderConfig();
+
+    return id(new PhutilAuthAdapterOAuthMediaWiki())
+      ->setAdapterDomain($config->getProviderDomain())
+      ->setMediaWikiBaseURI(
+        $config->getProperty(self::PROPERTY_MEDIAWIKI_URI));
+  }
+
+  protected function getLoginIcon() {
+    return 'MediaWiki';
+  }
+
+  private function isSetup() {
+    return !$this->getProviderConfig()->getID();
+  }
+
+  public function processEditForm(
+    AphrontRequest $request,
+    array $values) {
+    $errors = array();
+    $issues = array();
+
+    $is_setup = $this->isSetup();
+
+    $key_name = self::PROPERTY_MEDIAWIKI_NAME;
+    $key_uri = self::PROPERTY_MEDIAWIKI_URI;
+    $key_secret = self::PROPERTY_CONSUMER_SECRET;
+    $key_consumer = self::PROPERTY_CONSUMER_KEY;
+
+    if (!strlen($values[$key_uri])) {
+      $errors[] = pht('MediaWiki base URI is required.');
+      $issues[$key_uri] = pht('Required');
+    } else {
+      $uri = new PhutilURI($values[$key_uri]);
+      if (!$uri->getProtocol()) {
+        $errors[] = pht(
+          'MediaWiki base URI should include protocol '
+         .'(like "https://").');
+        $issues[$key_uri] = pht('Invalid');
+      }
+    }
+
+    if (!$errors) {
+      $config = $this->getProviderConfig();
+      if ($is_setup) {
+        $config->setProviderDomain($values[$key_name]);
+        $config->setProperty($key_name, $values[$key_name]);
+      }
+
+      $config->setProperty($key_uri, $values[$key_uri]);
+      $config->setProperty($key_secret, $values[$key_secret]);
+      $config->setProperty($key_consumer, $values[$key_consumer]);
+    }
+
+    return array($errors, $issues, $values);
+  }
+
+  public function extendEditForm(
+    AphrontRequest $request,
+    AphrontFormView $form,
+    array $values,
+    array $issues) {
+
+    $is_setup = $this->isSetup();
+
+    $e_required = $request->isFormPost() ? null : true;
+
+    $v_name = $values[self::PROPERTY_MEDIAWIKI_NAME];
+    if ($is_setup) {
+      $e_name = idx($issues, self::PROPERTY_MEDIAWIKI_NAME, $e_required);
+    } else {
+      $e_name = null;
+    }
+
+    $v_uri = $values[self::PROPERTY_MEDIAWIKI_URI];
+    $e_uri = idx($issues, self::PROPERTY_MEDIAWIKI_URI, $e_required);
+
+    $config = $this->getProviderConfig();
+
+    if ($is_setup) {
+      $form
+        ->appendRemarkupInstructions(
+          pht(
+            "**MediaWiki Instance Name**\n\n".
+            "Choose a permanent name for this instance of MediaWiki.".
+            "Phabricator uses this name internally to keep track of ".
+            "this instance of MediaWiki, in case the URL changes later.".
+            "\n\n".
+            "Use lowercase letters, digits, and period. For example: ".
+            "\n\n`mediawiki`, `mediawiki.mycompany` ".
+            "or `mediawiki.engineering` are reasonable names."))
+        ->appendChild(
+          id(new AphrontFormTextControl())
+            ->setLabel(pht('MediaWiki Instance Name'))
+            ->setValue($v_name)
+            ->setName(self::PROPERTY_MEDIAWIKI_NAME)
+            ->setError($e_name));
+    } else {
+      $form
+        ->appendChild(
+          id(new AphrontFormStaticControl())
+            ->setLabel(pht('MediaWiki Instance Name'))
+            ->setValue($v_name));
+    }
+
+    $form
+      ->appendChild(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('MediaWiki Base URI'))
+          ->setValue($v_uri)
+          ->setName(self::PROPERTY_MEDIAWIKI_URI)
+          ->setCaption(pht('The URI where MediaWiki is installed.'))
+          ->setError($e_uri))
+      ->appendRemarkupInstructions(
+        pht(
+          'NOTE: Copy the keys generated by the MediaWiki OAuth'.
+          ' consumer registration and paste them here.'))
+      ->appendChild(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('Consumer Key'))
+          ->setName(self::PROPERTY_CONSUMER_KEY)
+          ->setValue(
+            $config->getProperty(self::PROPERTY_CONSUMER_KEY)))
+      ->appendChild(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('Secret Key'))
+          ->setName(self::PROPERTY_CONSUMER_SECRET)
+          ->setValue(
+            $config->getProperty(self::PROPERTY_CONSUMER_SECRET)));
+  }
+
+  public static function getMediaWikiProvider() {
+    $providers = self::getAllEnabledProviders();
+
+    foreach ($providers as $provider) {
+      if ($provider instanceof PhabricatorAuthProviderOAuth1MediaWiki) {
+        return $provider;
+      }
+    }
+
+    return null;
+  }
+
+}