diff --git a/src/Services/OAuth/OAuthClientAdminManager.php b/src/Services/OAuth/OAuthClientAdminManager.php
new file mode 100644
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--- /dev/null
+++ b/src/Services/OAuth/OAuthClientAdminManager.php
@@ -0,0 +1,133 @@
+<?php
+/*
+ * This file is part of Part-DB (https://github.com/Part-DB/Part-DB-symfony).
+ *
+ *  Copyright (C) 2019 - 2026 Jan Böhmer (https://github.com/jbtronics)
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as published
+ *  by the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace App\Services\OAuth;
+
+use Doctrine\ORM\EntityManagerInterface;
+use League\Bundle\OAuth2ServerBundle\Manager\ClientManagerInterface;
+use League\Bundle\OAuth2ServerBundle\Model\AbstractClient;
+use League\Bundle\OAuth2ServerBundle\Model\AccessToken;
+use League\Bundle\OAuth2ServerBundle\Model\AuthorizationCode;
+use League\Bundle\OAuth2ServerBundle\Model\ClientInterface;
+use League\Bundle\OAuth2ServerBundle\Model\RefreshToken;
+
+/**
+ * Backs the admin OAuth2 client overview (App\Controller\OAuthClientAdminController) - listing every
+ * registered client (almost always RFC 7591 self-registered, see that controller's docblock) with how
+ * many currently-live access tokens each one holds, and permanently removing a client plus everything it
+ * was ever granted.
+ *
+ * Deliberately does NOT use League\Bundle\OAuth2ServerBundle\Service\CredentialsRevokerInterface's
+ * DoctrineCredentialsRevoker: it unconditionally also issues an UPDATE against the DeviceCode model/table,
+ * which does not exist in our schema (config/packages/league_oauth2_server.yaml disables the device code
+ * grant, so migrations/Version20260726180454.php never created oauth2_device_code) - that call would
+ * throw "no such table" here. The access/refresh tokens and authorization codes (the 3 credential types
+ * we actually persist) are bulk-deleted directly instead, before removing the client itself - the
+ * "client" FK columns are mapped ON DELETE CASCADE (see League's Persistence\Mapping\Driver), but SQLite
+ * only enforces that when "PRAGMA foreign_keys = ON" is set on the connection, which is not guaranteed
+ * here, so this does not rely on it.
+ */
+class OAuthClientAdminManager
+{
+    public function __construct(
+        private readonly EntityManagerInterface $entityManager,
+        private readonly ClientManagerInterface $clientManager,
+    ) {
+    }
+
+    /**
+     * @return list<array{client: ClientInterface, liveTokenCount: int}>
+     */
+    public function listClientsWithLiveTokenCounts(): array
+    {
+        $clients = $this->clientManager->list(null);
+
+        $rows = $this->entityManager->createQueryBuilder()
+            ->select('IDENTITY(at.client) as clientId', 'COUNT(at.identifier) as tokenCount')
+            ->from(AccessToken::class, 'at')
+            ->where('at.revoked = false')
+            ->andWhere('at.expiry > :now')
+            ->groupBy('at.client')
+            ->setParameter('now', new \DateTimeImmutable())
+            ->getQuery()
+            ->getResult();
+
+        /** @var array<string, int> $countByClientId */
+        $countByClientId = [];
+        foreach ($rows as $row) {
+            $countByClientId[$row['clientId']] = (int) $row['tokenCount'];
+        }
+
+        return array_map(static fn (ClientInterface $client): array => [
+            'client' => $client,
+            'liveTokenCount' => $countByClientId[$client->getIdentifier()] ?? 0,
+        ], $clients);
+    }
+
+    /**
+     * @return bool false if no client with that identifier exists
+     */
+    public function deleteClient(string $identifier): bool
+    {
+        $client = $this->clientManager->find($identifier);
+        if (!$client instanceof AbstractClient) {
+            return false;
+        }
+
+        $this->deleteAllCredentialsForClient($identifier);
+        $this->clientManager->remove($client);
+
+        return true;
+    }
+
+    private function deleteAllCredentialsForClient(string $clientIdentifier): void
+    {
+        // Refresh tokens first - they reference access tokens (not the client directly), so this has to
+        // run before the access tokens themselves are deleted.
+        $accessTokenIdsSubQuery = $this->entityManager->createQueryBuilder()
+            ->select('at2.identifier')
+            ->from(AccessToken::class, 'at2')
+            ->where('at2.client = :client')
+            ->getDQL();
+
+        $refreshTokenDelete = $this->entityManager->createQueryBuilder();
+        $refreshTokenDelete->delete(RefreshToken::class, 'rt')
+            ->where($refreshTokenDelete->expr()->in('rt.accessToken', $accessTokenIdsSubQuery))
+            ->setParameter('client', $clientIdentifier)
+            ->getQuery()
+            ->execute();
+
+        $this->entityManager->createQueryBuilder()
+            ->delete(AccessToken::class, 'at')
+            ->where('at.client = :client')
+            ->setParameter('client', $clientIdentifier)
+            ->getQuery()
+            ->execute();
+
+        $this->entityManager->createQueryBuilder()
+            ->delete(AuthorizationCode::class, 'ac')
+            ->where('ac.client = :client')
+            ->setParameter('client', $clientIdentifier)
+            ->getQuery()
+            ->execute();
+    }
+}