Generalize login flows for new registration

Summary:
Ref T1536. None of this code is reachable.

`PhabricatorAuthLoginController` provides a completely generic login/link flow, similar to how D6155 provides a generic registration flow.

`PhabricatorAuthProvider` wraps a `PhutilAuthAdapter` and glues the generic top-level flow to a concrete authentication provider.

Test Plan: Static only, code isn't meaningfully reachable.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1536

Differential Revision: https://secure.phabricator.com/D6159

src/applications/auth/controller/PhabricatorAuthLoginController.php

@@ -0,0 +1,160 @@
+<?php
+
+final class PhabricatorAuthLoginController
+  extends PhabricatorAuthController {
+
+  private $providerKey;
+  private $provider;
+
+  public function shouldRequireLogin() {
+    return false;
+  }
+
+  public function willProcessRequest(array $data) {
+    $this->providerKey = $data['pkey'];
+  }
+
+  public function processRequest() {
+    $request = $this->getRequest();
+    $viewer = $request->getUser();
+
+    $response = $this->loadProvider();
+    if ($response) {
+      return $response;
+    }
+
+    $provider = $this->provider;
+
+    list($account, $response) = $provider->processLoginRequest($this);
+    if ($response) {
+      return $response;
+    }
+
+    if ($account->getUserPHID()) {
+      // The account is already attached to a Phabricator user, so this is
+      // either a login or a bad account link request.
+      if (!$viewer->isLoggedIn()) {
+        if ($provider->shouldAllowLogin()) {
+          return $this->processLoginUser($account);
+        } else {
+          return $this->renderError(
+            pht(
+              'The external account ("%s") you just authenticated with is '.
+              'not configured to allow logins on this Phabricator install. '.
+              'An administrator may have recently disabled it.',
+              $provider->getProviderName()));
+        }
+      } else if ($viewer->getPHID() == $account->getUserPHID()) {
+        return $this->renderError(
+          pht(
+            'This external account ("%s") is already linked to your '.
+            'Phabricator account.'));
+      } else {
+        return $this->renderError(
+          pht(
+            'The external account ("%s") you just used to login is alerady '.
+            'associated with another Phabricator user account. Login to the '.
+            'other Phabricator account and unlink the external account before '.
+            'linking it to a new Phabricator account.',
+            $provider->getProviderName()));
+      }
+    } else {
+      // The account is not yet attached to a Phabricator user, so this is
+      // either a registration or an account link request.
+      if (!$viewer->isLoggedIn()) {
+        if ($provider->shouldAllowRegistration()) {
+          return $this->processRegisterUser($account);
+        } else {
+          return $this->renderError(
+            pht(
+              'The external account ("%s") you just authenticated with is '.
+              'not configured to allow registration on this Phabricator '.
+              'install. An administrator may have recently disabled it.',
+              $provider->getProviderName()));
+        }
+      } else {
+        if ($provider->shouldAllowAccountLink()) {
+          return $this->processLinkUser($account);
+        } else {
+          return $this->renderError(
+            pht(
+              'The external account ("%s") you just authenticated with is '.
+              'not configured to allow account linking on this Phabricator '.
+              'install. An administrator may have recently disabled it.'));
+        }
+      }
+    }
+
+    // This should be unreachable, but fail explicitly if we get here somehow.
+    return new Aphront400Response();
+  }
+
+  private function processLoginUser(PhabricatorExternalAccount $account) {
+    // TODO: Implement.
+    return new Aphront404Response();
+  }
+
+  private function processRegisterUser(PhabricatorExternalAccount $account) {
+    if ($account->getUserPHID()) {
+      throw new Exception("Account is already registered.");
+    }
+
+    // Regenerate the registration secret key, set it on the external account,
+    // set a cookie on the user's machine, and redirect them to registration.
+    // See PhabricatorAuthRegisterController for discussion of the registration
+    // key.
+
+    $registration_key = Filesystem::readRandomCharacters(32);
+    $account->setProperty('registrationKey', $registration_key);
+
+    $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+      $account->save();
+    unset($unguarded);
+
+    $this->getRequest()->setCookie('phreg', $registration_key);
+
+    $account_secret = $account->getAccountSecret();
+    $register_uri = $this->getApplicationURI('register/'.$account_secret.'/');
+    return id(new AphrontRedirectResponse())->setURI($register_uri);
+  }
+
+  private function processLinkUser(PhabricatorExternalAccount $account) {
+    // TODO: Implement.
+    return new Aphront404Response();
+  }
+
+  private function loadProvider() {
+    $provider = PhabricatorAuthProvider::getEnabledProviderByKey(
+      $this->providerKey);
+
+    if (!$provider) {
+      return $this->renderError(
+        pht(
+          'The account you are attempting to login with uses a nonexistent '.
+          'or disabled authentication provider (with key "%s"). An '.
+          'administrator may have recently disabled this provider.',
+          $this->providerKey));
+    }
+
+    $this->provider = $provider;
+
+    return null;
+  }
+
+  private function renderError($message) {
+    $title = pht('Login Failed');
+
+    $view = new AphrontErrorView();
+    $view->setTitle($title);
+    $view->appendChild($message);
+
+    return $this->buildApplicationPage(
+      $view,
+      array(
+        'title' => $title,
+        'device' => true,
+        'dust' => true,
+      ));
+  }
+
+}