diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index b18cd32d16..a115a46109 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -815,6 +815,7 @@ phutil_register_library_map(array(
     'PhabricatorAuditReplyHandler' => 'applications/audit/mail/PhabricatorAuditReplyHandler.php',
     'PhabricatorAuditStatusConstants' => 'applications/audit/constants/PhabricatorAuditStatusConstants.php',
     'PhabricatorAuthController' => 'applications/auth/controller/PhabricatorAuthController.php',
+    'PhabricatorAuthRegisterController' => 'applications/auth/controller/PhabricatorAuthRegisterController.php',
     'PhabricatorAuthenticationConfigOptions' => 'applications/config/option/PhabricatorAuthenticationConfigOptions.php',
     'PhabricatorBarePageExample' => 'applications/uiexample/examples/PhabricatorBarePageExample.php',
     'PhabricatorBarePageView' => 'view/page/PhabricatorBarePageView.php',
@@ -1335,6 +1336,7 @@ phutil_register_library_map(array(
     'PhabricatorRecaptchaConfigOptions' => 'applications/config/option/PhabricatorRecaptchaConfigOptions.php',
     'PhabricatorRedirectController' => 'applications/base/controller/PhabricatorRedirectController.php',
     'PhabricatorRefreshCSRFController' => 'applications/auth/controller/PhabricatorRefreshCSRFController.php',
+    'PhabricatorRegistrationProfile' => 'applications/people/storage/PhabricatorRegistrationProfile.php',
     'PhabricatorRemarkupControl' => 'view/form/control/PhabricatorRemarkupControl.php',
     'PhabricatorRemarkupRuleEmbedFile' => 'applications/files/remarkup/PhabricatorRemarkupRuleEmbedFile.php',
     'PhabricatorRemarkupRuleImageMacro' => 'applications/macro/remarkup/PhabricatorRemarkupRuleImageMacro.php',
@@ -2667,6 +2669,7 @@ phutil_register_library_map(array(
     'PhabricatorAuditPreviewController' => 'PhabricatorAuditController',
     'PhabricatorAuditReplyHandler' => 'PhabricatorMailReplyHandler',
     'PhabricatorAuthController' => 'PhabricatorController',
+    'PhabricatorAuthRegisterController' => 'PhabricatorAuthController',
     'PhabricatorAuthenticationConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorBarePageExample' => 'PhabricatorUIExample',
     'PhabricatorBarePageView' => 'AphrontPageView',
@@ -3182,6 +3185,7 @@ phutil_register_library_map(array(
     'PhabricatorRecaptchaConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorRedirectController' => 'PhabricatorController',
     'PhabricatorRefreshCSRFController' => 'PhabricatorAuthController',
+    'PhabricatorRegistrationProfile' => 'Phobject',
     'PhabricatorRemarkupControl' => 'AphrontFormTextAreaControl',
     'PhabricatorRemarkupRuleEmbedFile' => 'PhutilRemarkupRule',
     'PhabricatorRemarkupRuleImageMacro' => 'PhutilRemarkupRule',
diff --git a/src/applications/auth/application/PhabricatorApplicationAuth.php b/src/applications/auth/application/PhabricatorApplicationAuth.php
index 37d9a3a82f..6fcce8ac23 100644
--- a/src/applications/auth/application/PhabricatorApplicationAuth.php
+++ b/src/applications/auth/application/PhabricatorApplicationAuth.php
@@ -29,4 +29,12 @@ final class PhabricatorApplicationAuth extends PhabricatorApplication {
     return $items;
   }
 
+  public function getRoutes() {
+    return array(
+      '/auth/' => array(
+        'register/(?P<akey>[^/]+)/' => 'PhabricatorAuthRegisterController',
+      ),
+    );
+  }
+
 }
diff --git a/src/applications/auth/controller/PhabricatorAuthController.php b/src/applications/auth/controller/PhabricatorAuthController.php
index 19094da148..9f6b76e468 100644
--- a/src/applications/auth/controller/PhabricatorAuthController.php
+++ b/src/applications/auth/controller/PhabricatorAuthController.php
@@ -14,4 +14,39 @@ abstract class PhabricatorAuthController extends PhabricatorController {
     return $response->setContent($page->render());
   }
 
+  protected function renderErrorPage($title, array $messages) {
+    $view = new AphrontErrorView();
+    $view->setTitle($title);
+    $view->setErrors($messages);
+
+    return $this->buildApplicationPage(
+      $view,
+      array(
+        'title' => $title,
+        'device' => true,
+        'dust' => true,
+      ));
+
+  }
+
+  protected function establishWebSession(PhabricatorUser $user) {
+    $session_key = $user->establishSession('web');
+
+    $request = $this->getRequest();
+
+    // NOTE: We allow disabled users to login and roadblock them later, so
+    // there's no check for users being disabled here.
+
+    $request->setCookie('phusr', $user->getUsername());
+    $request->setCookie('phsid', $session_key);
+    $request->clearCookie('phreg');
+  }
+
+  protected function buildLoginValidateResponse(PhabricatorUser $user) {
+    $validate_uri = new PhutilURI($this->getApplicationURI('validate/'));
+    $validate_uri->setQueryParam('phusr', $user->getUsername());
+
+    return id(new AphrontRedirectResponse())->setURI((string)$validate_uri);
+  }
+
 }
diff --git a/src/applications/auth/controller/PhabricatorAuthRegisterController.php b/src/applications/auth/controller/PhabricatorAuthRegisterController.php
new file mode 100644
index 0000000000..74cdb1cfe9
--- /dev/null
+++ b/src/applications/auth/controller/PhabricatorAuthRegisterController.php
@@ -0,0 +1,483 @@
+<?php
+
+final class PhabricatorAuthRegisterController
+  extends PhabricatorAuthController {
+
+  private $accountKey;
+  private $account;
+  private $provider;
+
+  public function shouldRequireLogin() {
+    return false;
+  }
+
+  public function willProcessRequest(array $data) {
+    $this->accountKey = idx($data, 'akey');
+  }
+
+  public function processRequest() {
+    $request = $this->getRequest();
+
+    if ($request->getUser()->isLoggedIn()) {
+      return $this->renderError(pht('You are already logged in.'));
+    }
+
+    if (strlen($this->accountKey)) {
+      $response = $this->loadAccount();
+    } else {
+      $response = $this->loadDefaultAccount();
+    }
+
+    if ($response) {
+      return $response;
+    }
+
+    $account = $this->account;
+
+    $user = new PhabricatorUser();
+
+    $default_username = $account->getUsername();
+    $default_realname = $account->getRealName();
+    $default_email = $account->getEmail();
+    if ($default_email) {
+      // If the account source provided an email but it's not allowed by
+      // the configuration, just pretend we didn't get an email at all.
+      if (!PhabricatorUserEmail::isAllowedAddress($default_email)) {
+        $default_email = null;
+      }
+
+      // If the account source provided an email, but another account already
+      // has that email, just pretend we didn't get an email.
+
+      // TODO: See T3340.
+
+      if ($default_email) {
+        $same_email = id(new PhabricatorUserEmail())->loadOneWhere(
+          'address = %s',
+          $default_email);
+        if ($same_email) {
+          $default_email = null;
+        }
+      }
+    }
+
+    $profile = id(new PhabricatorRegistrationProfile())
+      ->setDefaultUsername($default_username)
+      ->setDefaultEmail($default_email)
+      ->setDefaultRealName($default_realname)
+      ->setCanEditUsername(true)
+      ->setCanEditEmail(($default_email === null))
+      ->setCanEditRealName(true)
+      ->setShouldVerifyEmail(false);
+
+    $event_type = PhabricatorEventType::TYPE_AUTH_WILLREGISTERUSER;
+    $event_data = array(
+      'account' => $account,
+      'profile' => $profile,
+    );
+
+    $event = id(new PhabricatorEvent($event_type, $event_data))
+      ->setUser($user);
+    PhutilEventEngine::dispatchEvent($event);
+
+    $default_username = $profile->getDefaultUsername();
+    $default_email = $profile->getDefaultEmail();
+    $default_realname = $profile->getDefaultRealName();
+
+    $can_edit_username = $profile->getCanEditUsername();
+    $can_edit_email = $profile->getCanEditEmail();
+    $can_edit_realname = $profile->getCanEditRealName();
+
+    $must_set_password = $this->provider->shouldRequireRegistrationPassword();
+
+    $can_edit_anything = $profile->getCanEditAnything() || $must_set_password;
+    $force_verify = $profile->getShouldVerifyEmail();
+
+    $value_username = $default_username;
+    $value_realname = $default_realname;
+    $value_email = $default_email;
+    $value_password = null;
+
+    $errors = array();
+
+    $e_username = strlen($value_username) ? null : true;
+    $e_realname = strlen($value_realname) ? null : true;
+    $e_email = strlen($value_email) ? null : true;
+    $e_password = true;
+
+    $min_len = PhabricatorEnv::getEnvConfig('account.minimum-password-length');
+    $min_len = (int)$min_len;
+
+    if ($request->isFormPost() || !$can_edit_anything) {
+      $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+
+      if ($can_edit_username) {
+        $value_username = $request->getStr('username');
+        if (!strlen($value_username)) {
+          $e_username = pht('Required');
+          $errors[] = pht('Username is required.');
+        } else if (!PhabricatorUser::validateUsername($value_username)) {
+          $e_username = pht('Invalid');
+          $errors[] = PhabricatorUser::describeValidUsername();
+        } else {
+          $e_username = null;
+        }
+      }
+
+      if ($must_set_password) {
+        $value_password = $request->getStr('password');
+        $value_confirm = $request->getStr('confirm');
+        if (!strlen($value_password)) {
+          $e_password = pht('Required');
+          $errors[] = pht('You must choose a password.');
+        } else if ($value_password !== $value_confirm) {
+          $e_password = pht('No Match');
+          $errors[] = pht('Password and confirmation must match.');
+        } else if (strlen($value_password) < $min_len) {
+          $e_password = pht('Too Short');
+          $errors[] = pht(
+            'Password is too short (must be at least %d characters long).',
+            $min_len);
+        } else {
+          $e_password = null;
+        }
+      }
+
+      if ($can_edit_email) {
+        $value_email = $request->getStr('email');
+        if (!strlen($value_email)) {
+          $e_email = pht('Required');
+          $errors[] = pht('Email is required.');
+        } else if (!PhabricatorUserEmail::isAllowedAddress($value_email)) {
+          $e_email = pht('Invalid');
+          $errors[] = PhabricatorUserEmail::describeAllowedAddresses();
+        } else {
+          $e_email = null;
+        }
+      }
+
+      if ($can_edit_realname) {
+        $value_realname = $request->getStr('realName');
+        if (!strlen($value_realname)) {
+          $e_realname = pht('Required');
+          $errors[] = pht('Real name is required.');
+        } else {
+          $e_realname = null;
+        }
+      }
+
+      if (!$errors) {
+        $image = $this->loadProfilePicture($account);
+        if ($image) {
+          $user->setProfileImagePHID($image->getPHID());
+        }
+
+        try {
+          if ($force_verify) {
+            $verify_email = true;
+          } else {
+            $verify_email =
+              ($account->getEmailVerified()) &&
+              ($value_email === $default_email);
+          }
+
+          $email_obj = id(new PhabricatorUserEmail())
+            ->setAddress($value_email)
+            ->setIsVerified((int)$verify_email);
+
+          $user->setUsername($value_username);
+          $user->setRealname($value_realname);
+
+          $user->openTransaction();
+
+            $editor = id(new PhabricatorUserEditor())
+              ->setActor($user);
+
+            $editor->createNewUser($user, $email_obj);
+            if ($must_set_password) {
+              $envelope = new PhutilOpaqueEnvelope($value_password);
+              $editor->changePassword($user, $envelope);
+            }
+
+            $account->setUserPHID($user->getPHID());
+            $this->provider->willRegisterAccount($account);
+            $account->save();
+
+          $user->saveTransaction();
+
+          $this->establishWebSession($user);
+
+          if (!$email_obj->getIsVerified()) {
+            $email_obj->sendVerificationEmail($user);
+          }
+
+          return $this->buildLoginValidateResponse($user);
+        } catch (AphrontQueryDuplicateKeyException $exception) {
+          $same_username = id(new PhabricatorUser())->loadOneWhere(
+            'userName = %s',
+            $user->getUserName());
+
+          $same_email = id(new PhabricatorUserEmail())->loadOneWhere(
+            'address = %s',
+            $value_email);
+
+          if ($same_username) {
+            $e_username = pht('Duplicate');
+            $errors[] = pht('Another user already has that username.');
+          }
+
+          if ($same_email) {
+            // TODO: See T3340.
+            $e_email = pht('Duplicate');
+            $errors[] = pht('Another user already has that email.');
+          }
+
+          if (!$same_username && !$same_email) {
+            throw $exception;
+          }
+        }
+      }
+
+      unset($unguarded);
+    }
+
+    $error_view = null;
+    if ($errors) {
+      $error_view = new AphrontErrorView();
+      $error_view->setTitle(pht('Registration Failed'));
+      $error_view->setErrors($errors);
+    }
+
+    $form = id(new AphrontFormView())
+      ->setUser($request->getUser())
+      ->appendChild(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('Username'))
+          ->setName('username')
+          ->setValue($value_username)
+          ->setError($e_username));
+
+    if ($must_set_password) {
+      $form->appendChild(
+        id(new AphrontFormPasswordControl())
+          ->setLabel(pht('Password'))
+          ->setName('password')
+          ->setError($e_password)
+          ->setCaption(
+            $min_len
+              ? pht('Minimum length of %d characters.', $min_len)
+              : null));
+      $form->appendChild(
+        id(new AphrontFormPasswordControl())
+          ->setLabel(pht('Confirm Password'))
+          ->setName('confirm')
+          ->setError($e_password));
+    }
+
+    if ($can_edit_email) {
+      $form->appendChild(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('Email'))
+          ->setName('email')
+          ->setValue($value_email)
+          ->setCaption(PhabricatorUserEmail::describeAllowedAddresses())
+          ->setError($e_email));
+    }
+
+    if ($can_edit_realname) {
+      $form->appendChild(
+        id(new AphrontFormTextControl())
+          ->setLabel(pht('Real Name'))
+          ->setName('realName')
+          ->setValue($value_realname)
+          ->setError($e_realname));
+    }
+
+    $form->appendChild(
+      id(new AphrontFormSubmitControl())
+        ->setValue(pht('Create Account')));
+
+    $title = pht('Phabricator Registration');
+
+    $crumbs = $this->buildApplicationCrumbs();
+    $crumbs->addCrumb(
+      id(new PhabricatorCrumbView())
+        ->setName(pht('Register')));
+
+    return $this->buildApplicationPage(
+      array(
+        $crumbs,
+        $error_view,
+        $form,
+      ),
+      array(
+        'title' => $title,
+        'device' => true,
+        'dust' => true,
+      ));
+  }
+
+  private function loadAccount() {
+    $request = $this->getRequest();
+
+    if (!$this->accountKey) {
+      return $this->renderError(pht('Request did not include account key.'));
+    }
+
+    $account = id(new PhabricatorExternalAccount())->loadOneWhere(
+      'accountSecret = %s',
+      $this->accountKey);
+
+    if (!$account) {
+      return $this->renderError(pht('No registration account.'));
+    }
+
+    if ($account->getUserPHID()) {
+      return $this->renderError(
+        pht(
+          'The account you are attempting to register with is already '.
+          'registered to another user.'));
+    }
+
+    $registration_key = $request->getCookie('phreg');
+
+    // NOTE: This registration key check is not strictly necessary, because
+    // we're only creating new accounts, not linking existing accounts. It
+    // might be more hassle than it is worth, especially for email.
+    //
+    // The attack this prevents is getting to the registration screen, then
+    // copy/pasting the URL and getting someone else to click it and complete
+    // the process. They end up with an account bound to credentials you
+    // control. This doesn't really let you do anything meaningful, though,
+    // since you could have simply completed the process yourself.
+
+    if (!$registration_key) {
+      return $this->renderError(
+        pht(
+          'Your browser did not submit a registration key with the request. '.
+          'You must use the same browser to begin and complete registration. '.
+          'Check that cookies are enabled and try again.'));
+    }
+
+    if ($registration_key != $account->getProperty('registrationKey')) {
+      return $this->renderError(
+        pht(
+          'Your browser submitted a different registration key than the one '.
+          'associated with this account. You may need to clear your cookies.'));
+    }
+
+    $other_account = id(new PhabricatorExternalAccount())->loadAllWhere(
+      'accountType = %s AND accountDomain = %s AND accountID = %s
+        AND id != %d',
+      $account->getAccountType(),
+      $account->getAccountDomain(),
+      $account->getAccountID(),
+      $account->getID());
+
+    if ($other_account) {
+      return $this->renderError(
+        pht(
+          'The account you are attempting to register with already belongs '.
+          'to another user.'));
+    }
+
+    $provider = PhabricatorAuthProvider::getEnabledProviderByKey(
+      $account->getProviderKey());
+
+    if (!$provider) {
+      return $this->renderError(
+        pht(
+          'The account you are attempting to register with uses a nonexistent '.
+          'or disabled authentication provider (with key "%s"). An '.
+          'administrator may have recently disabled this provider.',
+          $account->getProviderKey()));
+    }
+
+    if (!$provider->shouldAllowRegistration()) {
+
+      // TODO: This is a routine error if you click "Login" on an external
+      // auth source which doesn't allow registration. The error should be
+      // more tailored.
+
+      return $this->renderError(
+        pht(
+          'The account you are attempting to register with uses an '.
+          'authentication provider ("%s") which does not allow registration. '.
+          'An administrator may have recently disabled registration with this '.
+          'provider.',
+          $provider->getProviderName()));
+    }
+
+    $this->account = $account;
+    $this->provider = $provider;
+
+    return null;
+  }
+
+  private function loadDefaultAccount() {
+    $providers = PhabricatorAuthProvider::getAllEnabledProviders();
+    foreach ($providers as $key => $provider) {
+      if (!$provider->shouldAllowRegistration()) {
+        unset($providers[$key]);
+        continue;
+      }
+      if (!$provider->isDefaultRegistrationProvider()) {
+        unset($providers[$key]);
+      }
+    }
+
+    if (!$providers) {
+      return $this->renderError(
+        pht(
+          "There are no configured default registration providers."));
+    } else if (count($providers) > 1) {
+      return $this->renderError(
+        pht(
+          "There are too many configured default registration providers."));
+    }
+
+    $this->account = $provider->getDefaultExternalAccount();
+    $this->provider = $provider;
+    return null;
+  }
+
+  private function loadProfilePicture(PhabricatorExternalAccount $account) {
+    $phid = $account->getProfileImagePHID();
+    if (!$phid) {
+      return null;
+    }
+
+    // NOTE: Use of omnipotent user is okay here because the registering user
+    // can not control the field value, and we can't use their user object to
+    // do meaningful policy checks anyway since they have not registered yet.
+    // Reaching this means the user holds the account secret key and the
+    // registration secret key, and thus has permission to view the image.
+
+    $file = id(new PhabricatorFileQuery())
+      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->withPHIDs(array($phid))
+      ->executeOne();
+    if (!$file) {
+      return null;
+    }
+
+    try {
+      $xformer = new PhabricatorImageTransformer();
+      return $xformer->executeProfileTransform(
+        $file,
+        $width = 50,
+        $min_height = 50,
+        $max_height = 50);
+    } catch (Exception $ex) {
+      phlog($ex);
+      return null;
+    }
+  }
+
+  private function renderError($message) {
+    return $this->renderErrorPage(
+      pht('Registration Failed'),
+      array($message));
+  }
+
+}
diff --git a/src/applications/people/storage/PhabricatorRegistrationProfile.php b/src/applications/people/storage/PhabricatorRegistrationProfile.php
new file mode 100644
index 0000000000..6a901c0b13
--- /dev/null
+++ b/src/applications/people/storage/PhabricatorRegistrationProfile.php
@@ -0,0 +1,84 @@
+<?php
+
+final class PhabricatorRegistrationProfile extends Phobject {
+
+  private $defaultUsername;
+  private $defaultEmail;
+  private $defaultRealName;
+  private $canEditUsername;
+  private $canEditEmail;
+  private $canEditRealName;
+  private $shouldVerifyEmail;
+
+  public function setShouldVerifyEmail($should_verify_email) {
+    $this->shouldVerifyEmail = $should_verify_email;
+    return $this;
+  }
+
+  public function getShouldVerifyEmail() {
+    return $this->shouldVerifyEmail;
+  }
+
+  public function setCanEditEmail($can_edit_email) {
+    $this->canEditEmail = $can_edit_email;
+    return $this;
+  }
+
+  public function getCanEditEmail() {
+    return $this->canEditEmail;
+  }
+
+  public function setCanEditRealName($can_edit_real_name) {
+    $this->canEditRealName = $can_edit_real_name;
+    return $this;
+  }
+
+  public function getCanEditRealName() {
+    return $this->canEditRealName;
+  }
+
+
+  public function setCanEditUsername($can_edit_username) {
+    $this->canEditUsername = $can_edit_username;
+    return $this;
+  }
+
+  public function getCanEditUsername() {
+    return $this->canEditUsername;
+  }
+
+  public function setDefaultEmail($default_email) {
+    $this->defaultEmail = $default_email;
+    return $this;
+  }
+
+  public function getDefaultEmail() {
+    return $this->defaultEmail;
+  }
+
+  public function setDefaultRealName($default_real_name) {
+    $this->defaultRealName = $default_real_name;
+    return $this;
+  }
+
+  public function getDefaultRealName() {
+    return $this->defaultRealName;
+  }
+
+
+  public function setDefaultUsername($default_username) {
+    $this->defaultUsername = $default_username;
+    return $this;
+  }
+
+  public function getDefaultUsername() {
+    return $this->defaultUsername;
+  }
+
+  public function getCanEditAnything() {
+    return $this->getCanEditUsername() ||
+           $this->getCanEditEmail() ||
+           $this->getCanEditRealName();
+  }
+
+}
diff --git a/src/infrastructure/events/constant/PhabricatorEventType.php b/src/infrastructure/events/constant/PhabricatorEventType.php
index 3d35e00476..a1b5bb3494 100644
--- a/src/infrastructure/events/constant/PhabricatorEventType.php
+++ b/src/infrastructure/events/constant/PhabricatorEventType.php
@@ -36,4 +36,6 @@ final class PhabricatorEventType extends PhutilEventType {
   const TYPE_UI_DIDRENDERHOVERCARD          = 'ui.didRenderHovercard';
 
   const TYPE_PEOPLE_DIDRENDERMENU           = 'people.didRenderMenu';
+  const TYPE_AUTH_WILLREGISTERUSER          = 'auth.willRegisterUser';
+
 }