Handle user aborts during auth workflows in Phabricator

Summary: Depends on D6872. Ref T3687. Give the user a nice dialog instead of a bare exception.

Test Plan: Cancelled out of Twitter and JIRA workflows. We should probably do this for the OAuth2 workflows too, but they're a bit of a pain to de-auth and I am lazy.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3687

Differential Revision: https://secure.phabricator.com/D6873

src/applications/auth/controller/PhabricatorAuthLoginController.php

@@ -25,7 +25,28 @@ final class PhabricatorAuthLoginController
 
     $provider = $this->provider;
 
+    try {
       list($account, $response) = $provider->processLoginRequest($this);
+    } catch (PhutilAuthUserAbortedException $ex) {
+      if ($viewer->isLoggedIn()) {
+        // If a logged-in user cancels, take them back to the external accounts
+        // panel.
+        $next_uri = '/settings/panel/external/';
+      } else {
+        // If a logged-out user cancels, take them back to the auth start page.
+        $next_uri = '/';
+      }
+
+      // User explicitly hit "Cancel".
+      $dialog = id(new AphrontDialogView())
+        ->setUser($viewer)
+        ->setTitle(pht('Authentication Canceled'))
+        ->appendChild(
+          pht('You canceled authentication.'))
+        ->addCancelButton($next_uri, pht('Continue'));
+      return id(new AphrontDialogResponse())->setDialog($dialog);
+    }
+
     if ($response) {
       return $response;
     }

src/applications/auth/provider/PhabricatorAuthProviderOAuth1.php

@@ -103,6 +103,13 @@ abstract class PhabricatorAuthProviderOAuth1 extends PhabricatorAuthProvider {
       return array($account, $response);
     }
 
+    $denied = $request->getStr('denied');
+    if (strlen($denied)) {
+      // Twitter indicates that the user cancelled the login attempt by
+      // returning "denied" as a parameter.
+      throw new PhutilAuthUserAbortedException();
+    }
+
     // NOTE: You can get here via GET, this should probably be a bit more
     // user friendly.