Support Twitch.tv as an OAuth provider

Summary:
This is mostly for personal reasons / lols, but they have a perfectly functional OAuth2 API and it takes like 15 minutes to add a provider now and I was in this code anyway...

@chad, we could use JIRA, Twitter and Twitch.tv auth icons if you have a chance.

Test Plan: {F53564}

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6706

src/__phutil_library_map__.php

@@ -901,6 +901,7 @@ phutil_register_library_map(array(
     'PhabricatorAuthProviderOAuthFacebook' => 'applications/auth/provider/PhabricatorAuthProviderOAuthFacebook.php',
     'PhabricatorAuthProviderOAuthGitHub' => 'applications/auth/provider/PhabricatorAuthProviderOAuthGitHub.php',
     'PhabricatorAuthProviderOAuthGoogle' => 'applications/auth/provider/PhabricatorAuthProviderOAuthGoogle.php',
+    'PhabricatorAuthProviderOAuthTwitch' => 'applications/auth/provider/PhabricatorAuthProviderOAuthTwitch.php',
     'PhabricatorAuthProviderPassword' => 'applications/auth/provider/PhabricatorAuthProviderPassword.php',
     'PhabricatorAuthRegisterController' => 'applications/auth/controller/PhabricatorAuthRegisterController.php',
     'PhabricatorAuthStartController' => 'applications/auth/controller/PhabricatorAuthStartController.php',
@@ -2939,6 +2940,7 @@ phutil_register_library_map(array(
     'PhabricatorAuthProviderOAuthFacebook' => 'PhabricatorAuthProviderOAuth',
     'PhabricatorAuthProviderOAuthGitHub' => 'PhabricatorAuthProviderOAuth',
     'PhabricatorAuthProviderOAuthGoogle' => 'PhabricatorAuthProviderOAuth',
+    'PhabricatorAuthProviderOAuthTwitch' => 'PhabricatorAuthProviderOAuth',
     'PhabricatorAuthProviderPassword' => 'PhabricatorAuthProvider',
     'PhabricatorAuthRegisterController' => 'PhabricatorAuthController',
     'PhabricatorAuthStartController' => 'PhabricatorAuthController',

src/applications/auth/provider/PhabricatorAuthProviderOAuthTwitch.php

@@ -0,0 +1,36 @@
+<?php
+
+final class PhabricatorAuthProviderOAuthTwitch
+  extends PhabricatorAuthProviderOAuth {
+
+  public function getProviderName() {
+    return pht('Twitch.tv');
+  }
+
+  public function getConfigurationHelp() {
+    $login_uri = $this->getLoginURI();
+
+    return pht(
+      "To configure Twitch.tv OAuth, create a new application here:".
+      "\n\n".
+      "http://www.twitch.tv/settings/applications".
+      "\n\n".
+      "When creating your application, use these settings:".
+      "\n\n".
+      "  - **Redirect URI:** Set this to: `%s`".
+      "\n\n".
+      "After completing configuration, copy the **Client ID** and ".
+      "**Client Secret** to the fields above. (You may need to generate the ".
+      "client secret by clicking 'New Secret' first.)",
+      $login_uri);
+  }
+
+  protected function newOAuthAdapter() {
+    return new PhutilAuthAdapterOAuthTwitch();
+  }
+
+  protected function getLoginIcon() {
+    return 'Twitch';
+  }
+
+}