feat: identify accounts by a uuid in the oauth2 sub claim

src/Controller/Api/UserinfoController.php

@@ -58,7 +58,11 @@ class UserinfoController extends AbstractController
             // addresses on a person's record as a login and answers all of them with the same
             // ids and the same first contact address, so only the local account tells the staff
             // account and the private one apart — and they hold different roles.
-            $data->subject = (string) $user->getId();
+            //
+            // The uuid, not the primary key: consumers store this value and match their own
+            // accounts on it, so it must not disclose how many accounts exist or let one
+            // account's identifier be guessed from another's.
+            $data->subject = $user->getUuid();
             $data->loginEmail = $user->getEmail();
 
             // Patch current user's roles. The implicit ROLE_USER says nothing about the

src/Entity/User.php

@@ -6,6 +6,7 @@ use App\Repository\UserRepository;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface;
 use Symfony\Component\Security\Core\User\UserInterface;
+use Symfony\Component\Uid\Uuid;
 
 #[ORM\Entity(repositoryClass: UserRepository::class)]
 class User implements UserInterface, PasswordAuthenticatedUserInterface
@@ -15,6 +16,22 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
     #[ORM\Column(type: 'integer')]
     private ?int $id = null;
 
+    /**
+     * The account's external identifier, exported as the OAuth2 `sub` claim.
+     *
+     * Separate from the primary key on purpose: `sub` is handed to other applications, which
+     * store it and match their own accounts on it, so it has to be stable, unique and free of
+     * anything the row's position in the table implies. The auto-increment id satisfied the
+     * first two and neither of the last: it disclosed how many accounts exist and made one
+     * account's identifier a guess away from the next.
+     *
+     * v4 rather than the framework's default v7 (see config/packages/uid.yaml): v7 embeds its
+     * creation timestamp and sorts, which is useful for a key and is exactly the leak this
+     * column exists to avoid. Matches Groups\AccommodationBooking::$uuid in shape and version.
+     */
+    #[ORM\Column(type: 'string', length: 36, unique: true)]
+    private string $uuid;
+
     #[ORM\Column(type: 'string', length: 180, unique: true)]
     private ?string $email;
 
@@ -54,6 +71,7 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
     public function __construct(string $email)
     {
         $this->email = $email;
+        $this->uuid = Uuid::v4()->toRfc4122();
     }
 
     public function getId(): ?int
@@ -61,6 +79,11 @@ class User implements UserInterface, PasswordAuthenticatedUserInterface
         return $this->id;
     }
 
+    public function getUuid(): string
+    {
+        return $this->uuid;
+    }
+
     public function getEmail(): ?string
     {
         return $this->email;