Support invites in the registration and login flow

Summary:
Ref T7152. This substantially completes the upstream login flow. Basically, we just cookie you and push you through normal registration, with slight changes:

  - All providers allow registration if you have an invite.
  - Most providers get minor text changes to say "Register" instead of "Login" or "Login or Register".
  - The Username/Password provider changes to just a "choose a username" form.
  - We show the user that they're accepting an invite, and who invited them.

Then on actual registration:

  - Accepting an invite auto-verifies the address.
  - Accepting an invite auto-approves the account.
  - Your email is set to the invite email and locked.
  - Invites get to reassign nonprimary, unverified addresses from other accounts.

But 98% of the code is the same.

Test Plan:
  - Accepted an invite.
  - Verified a new address on an existing account via invite.
  - Followed a bad invite link.
  - Tried to accept a verified invite.
  - Reassigned an email by accepting an unverified, nonprimary invite on a new account.
  - Verified that reassigns appear in the activity log.

{F291493}
{F291494}
{F291495}
{F291496}
{F291497}
{F291498}
{F291499}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7152

Differential Revision: https://secure.phabricator.com/D11737

src/applications/auth/controller/PhabricatorAuthInviteController.php

@@ -17,8 +17,10 @@ final class PhabricatorAuthInviteController
       $engine->setUserHasConfirmedVerify(true);
     }
 
+    $invite_code = $request->getURIData('code');
+
     try {
-      $invite = $engine->processInviteCode($request->getURIData('code'));
+      $invite = $engine->processInviteCode($invite_code);
     } catch (PhabricatorAuthInviteDialogException $ex) {
       $response = $this->newDialog()
         ->setTitle($ex->getTitle())
@@ -48,10 +50,13 @@ final class PhabricatorAuthInviteController
       return id(new AphrontRedirectResponse())->setURI('/');
     }
 
+    // Give the user a cookie with the invite code and send them through
+    // normal registration. We'll adjust the flow there.
+    $request->setCookie(
+      PhabricatorCookies::COOKIE_INVITE,
+      $invite_code);
 
-    // TODO: This invite is good, but we need to drive the user through
-    // registration.
-    throw new Exception(pht('TODO: Build invite/registration workflow.'));
+    return id(new AphrontRedirectResponse())->setURI('/auth/start/');
   }