diff --git a/lib/Controller/LoginController.php b/lib/Controller/LoginController.php
index 04778e4f..071f50db 100644
--- a/lib/Controller/LoginController.php
+++ b/lib/Controller/LoginController.php
@@ -56,6 +56,7 @@
 use OCP\IURLGenerator;
 use OCP\IUserManager;
 use OCP\IUserSession;
+use OCP\LDAP\Exceptions\MultipleUsersReturnedException;
 use OCP\Security\ICrypto;
 use OCP\Security\ISecureRandom;
 use OCP\Session\Exceptions\SessionNotAvailableException;
@@ -634,14 +635,28 @@ public function code(string $state = '', string $code = '', string $scope = '',
 		$softAutoProvisionAllowed = (!isset($oidcSystemConfig['soft_auto_provision']) || $oidcSystemConfig['soft_auto_provision']);
 
 		$shouldDoUserLookup = !$autoProvisionAllowed || ($softAutoProvisionAllowed && !$this->provisioningService->hasOidcUserProvisitioned($userId));
+		$existingUser = null;
 		if ($shouldDoUserLookup && $this->ldapService->isLDAPEnabled()) {
-			// in case user is provisioned by user_ldap, userManager->search() triggers an ldap search which syncs the results
-			// so new users will be directly available even if they were not synced before this login attempt
-			$this->userManager->search($userId, 1, 0);
-			$this->ldapService->syncUser($userId);
+			$ldapMappingAttribute = $this->providerService->getSetting($providerId, ProviderService::SETTING_LDAP_MAPPING_ATTRIBUTE);
+			if ($ldapMappingAttribute !== '') {
+				// Find a user in LDAP with a custom attribute equal to the user id given in OIDC
+				try {
+					$existingUser = $this->ldapService->findUserByAttribute($ldapMappingAttribute, $userId);
+				} catch (MultipleUsersReturnedException $e) {
+					$message = $this->l10n->t('The configured LDAP mapping attribute returned more than one users. Please contact an administrator.');
+					return $this->build403TemplateResponse($message, Http::STATUS_FORBIDDEN);
+				}
+			} else {
+				// in case user is provisioned by user_ldap, userManager->search() triggers an ldap search which syncs the results
+				// so new users will be directly available even if they were not synced before this login attempt
+				$this->userManager->search($userId, 1, 0);
+				$this->ldapService->syncUser($userId);
+			}
 		}
 
-		$existingUser = $this->userManager->get($userId);
+		if ($existingUser === null) {
+			$existingUser = $this->userManager->get($userId);
+		}
 		if ($existingUser !== null && $this->ldapService->isLdapDeletedUser($existingUser)) {
 			$existingUser = null;
 		}
diff --git a/lib/Service/LdapService.php b/lib/Service/LdapService.php
index a616bce6..c5ec419a 100644
--- a/lib/Service/LdapService.php
+++ b/lib/Service/LdapService.php
@@ -10,7 +10,9 @@
 namespace OCA\UserOIDC\Service;
 
 use OCP\App\IAppManager;
+use OCP\IConfig;
 use OCP\IUser;
+use OCP\LDAP\Exceptions\MultipleUsersReturnedException;
 use OCP\Server;
 use Psr\Container\ContainerExceptionInterface;
 use Psr\Log\LoggerInterface;
@@ -79,4 +81,15 @@ public function syncUser(string $userId): void {
 			$this->logger->debug('\OCA\User_LDAP\User_Proxy class not found');
 		}
 	}
+
+	/**
+	 * @throws MultipleUsersReturnedException
+	 */
+	public function findUserByAttribute(string $attribute, string $searchTerm): ?IUser {
+		if (version_compare(Server::get(IConfig::class)->getSystemValueString('version', '0.0.0'), '34.0.0', '>=')) {
+			$ldapUserProxy = Server::get(\OCA\User_LDAP\User_Proxy::class);
+			return $ldapUserProxy->getUserFromCustomAttribute($attribute, $searchTerm);
+		}
+		return null;
+	}
 }
diff --git a/lib/Service/ProviderService.php b/lib/Service/ProviderService.php
index f5a82a51..27fce4fd 100644
--- a/lib/Service/ProviderService.php
+++ b/lib/Service/ProviderService.php
@@ -61,6 +61,7 @@ class ProviderService {
 	public const SETTING_RESTRICT_LOGIN_TO_GROUPS = 'restrictLoginToGroups';
 	public const SETTING_AZURE_GROUP_NAMES = 'azureGroupNames';
 	public const SETTING_RESOLVE_NESTED_AND_FALLBACK_CLAIMS_MAPPING = 'nestedAndFallbackClaims';
+	public const SETTING_LDAP_MAPPING_ATTRIBUTE = 'mappingAttribute';
 
 	public const BOOLEAN_SETTINGS_DEFAULT_VALUES = [
 		self::SETTING_GROUP_PROVISIONING => false,
diff --git a/lib/User/Backend.php b/lib/User/Backend.php
index 9e120c16..1e9610fd 100644
--- a/lib/User/Backend.php
+++ b/lib/User/Backend.php
@@ -22,6 +22,7 @@
 use OCA\UserOIDC\User\Validator\SelfEncodedValidator;
 use OCA\UserOIDC\User\Validator\UserInfoValidator;
 use OCP\AppFramework\Db\DoesNotExistException;
+use OCP\AppFramework\Http;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\Authentication\IApacheBackend;
 use OCP\DB\Exception;
@@ -38,6 +39,7 @@
 use OCP\IUser;
 use OCP\IUserManager;
 use OCP\IUserSession;
+use OCP\LDAP\Exceptions\MultipleUsersReturnedException;
 use OCP\Server;
 use OCP\User\Backend\ABackend;
 use OCP\User\Backend\ICountUsersBackend;
@@ -334,13 +336,11 @@ public function getCurrentUserId(): string {
 
 						if ($autoProvisionAllowed) {
 							// look for user in other backends
-							if (!$this->userManager->userExists($tokenUserId)) {
-								$this->userManager->search($tokenUserId);
-								$this->ldapService->syncUser($tokenUserId);
-							}
-							$existingUser = $this->userManager->get($tokenUserId);
-							if ($existingUser !== null && $this->ldapService->isLdapDeletedUser($existingUser)) {
-								$existingUser = null;
+							try {
+								$existingUser = $this->lookupUserInLDAP($provider, $tokenUserId);
+							} catch (MultipleUsersReturnedException $e) {
+								$this->logger->debug('The configured LDAP mapping attribute returned more than one users');
+								return '';
 							}
 
 							$softAutoProvisionAllowed = (!isset($oidcSystemConfig['soft_auto_provision']) || $oidcSystemConfig['soft_auto_provision']);
@@ -378,18 +378,13 @@ public function getCurrentUserId(): string {
 							// check if the user exists locally
 							// if not, this potentially triggers a user_ldap search
 							// to get the user if it has not been synced yet
-							if (!$this->userManager->userExists($tokenUserId)) {
-								$this->userManager->search($tokenUserId);
-								$this->ldapService->syncUser($tokenUserId);
-
-								// return nothing, if the user was not found after the user_ldap search
-								if (!$this->userManager->userExists($tokenUserId)) {
-									return '';
-								}
+							try {
+								$existingUser = $this->lookupUserInLDAP($provider, $tokenUserId);
+							} catch (MultipleUsersReturnedException $e) {
+								$this->logger->debug('The configured LDAP mapping attribute returned more than one users');
+								return '';
 							}
-
-							$user = $this->userManager->get($tokenUserId);
-							if ($user === null || $this->ldapService->isLdapDeletedUser($user)) {
+							if ($existingUser === null) {
 								return '';
 							}
 							$this->checkFirstLogin($tokenUserId);
@@ -406,6 +401,31 @@ public function getCurrentUserId(): string {
 		return '';
 	}
 
+	/**
+	 * @throws MultipleUsersReturnedException
+	 */
+	private function lookupUserInLDAP(Provider $provider, string $tokenUserId): ?IUser {
+		$existingUser = null;
+		if ($this->ldapService->isLDAPEnabled()) {
+			$ldapMappingAttribute = $this->providerService->getSetting($provider->getId(), ProviderService::SETTING_LDAP_MAPPING_ATTRIBUTE);
+			if ($ldapMappingAttribute !== '') {
+				// Find a user in LDAP with a custom attribute equal to the user id given in OIDC
+				$existingUser = $this->ldapService->findUserByAttribute($ldapMappingAttribute, $tokenUserId);
+			} else if (!$this->userManager->userExists($tokenUserId)) {
+				$this->userManager->search($tokenUserId);
+				$this->ldapService->syncUser($tokenUserId);
+			}
+
+			if ($existingUser === null) {
+				$existingUser = $this->userManager->get($tokenUserId);
+			}
+			if ($existingUser !== null && $this->ldapService->isLdapDeletedUser($existingUser)) {
+				$existingUser = null;
+			}
+		}
+		return $existingUser;
+	}
+
 	/**
 	 * Returns true only if $userId is a non-empty, non-whitespace-only string.
 	 * Used as a lightweight sanity check on user IDs returned by token validators