From b9c5bc8ec663a74d304015ca1d6b29f65b6df2e9 Mon Sep 17 00:00:00 2001
From: Carl Schwan <carl@carlschwan.eu>
Date: Wed, 22 Jul 2026 11:54:33 +0200
Subject: [PATCH] feat: Allow to check user existence outside specific user
 backends

Signed-off-by: Carl Schwan <carl@carlschwan.eu>
---
 lib/private/User/Manager.php        | 22 ++++++++++++++++------
 lib/public/IUserManager.php         |  5 +++--
 tests/Core/Command/User/AddTest.php |  5 +++++
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/lib/private/User/Manager.php b/lib/private/User/Manager.php
index 765e8fa3d7b7f..9bd1f20721fda 100644
--- a/lib/private/User/Manager.php
+++ b/lib/private/User/Manager.php
@@ -110,19 +110,25 @@ public function clearBackends(): void {
 	 * @param string $uid
 	 * @return \OC\User\User|null Either the user or null if the specified user does not exist
 	 */
-	public function get($uid) {
+	public function get($uid, array $excludeBackends = []) {
 		if (is_null($uid) || $uid === '' || $uid === false) {
 			return null;
 		}
-		if (isset($this->cachedUsers[$uid])) { //check the cache first to prevent having to loop over the backends
-			return $this->cachedUsers[$uid];
-		}
 
 		if (strlen($uid) > IUser::MAX_USERID_LENGTH) {
 			return null;
 		}
 
+		// check the cache first to prevent having to loop over the backends
+		if ($excludeBackends === [] && isset($this->cachedUsers[$uid])) {
+			return $this->cachedUsers[$uid];
+		}
+
 		$cachedBackend = $this->cache->get(sha1($uid));
+		if (in_array($cachedBackend, $excludeBackends)) {
+			$cachedBackend = null;
+		}
+
 		if ($cachedBackend !== null && isset($this->backends[$cachedBackend])) {
 			// Cache has the info of the user backend already, so ask that one directly
 			$backend = $this->backends[$cachedBackend];
@@ -137,6 +143,10 @@ public function get($uid) {
 				continue;
 			}
 
+			if (in_array($i, $excludeBackends)) {
+				continue;
+			}
+
 			if ($backend->userExists($uid)) {
 				// Hash $uid to ensure that only valid characters are used for the cache key
 				$this->cache->set(sha1($uid), $i, 300);
@@ -180,12 +190,12 @@ public function getUserObject($uid, $backend, $cacheUser = true) {
 	 * @param string $uid
 	 * @return bool
 	 */
-	public function userExists($uid) {
+	public function userExists($uid, array $excludeBackends = []) {
 		if (strlen($uid) > IUser::MAX_USERID_LENGTH) {
 			return false;
 		}
 
-		$user = $this->get($uid);
+		$user = $this->get($uid, $excludeBackends);
 		return ($user !== null);
 	}
 
diff --git a/lib/public/IUserManager.php b/lib/public/IUserManager.php
index 973e1c5ef4077..137d595767323 100644
--- a/lib/public/IUserManager.php
+++ b/lib/public/IUserManager.php
@@ -78,13 +78,14 @@ public function get($uid);
 	public function getDisplayName(string $uid): ?string;
 
 	/**
-	 * check if a user exists
+	 * Check if a user exists.
 	 *
 	 * @param string $uid
+	 * @param list<string> $excludeBackends A list of IUserBackend::getBackendName() that need to be excluded from the search.
 	 * @return bool
 	 * @since 8.0.0
 	 */
-	public function userExists($uid);
+	public function userExists($uid, array $excludeBackends = []);
 
 	/**
 	 * Check if the password is valid for the user
diff --git a/tests/Core/Command/User/AddTest.php b/tests/Core/Command/User/AddTest.php
index 5a8bc3abea1e9..42cc6ec198661 100644
--- a/tests/Core/Command/User/AddTest.php
+++ b/tests/Core/Command/User/AddTest.php
@@ -109,6 +109,11 @@ public function testAddEmail(
 		$this->mailHelper->expects($isEmailValid && $shouldSendEmail ? static::once() : static::never())
 			->method('sendMail');
 
+		$this->consoleInput->method('getArgument')
+			->willReturnMap([
+				['uid', 'JohnDoe'],
+			]);
+
 		$this->consoleInput->method('getOption')
 			->willReturnMap([
 				['generate-password', 'true'],