diff --git a/lib/private/Http/Client/ClientService.php b/lib/private/Http/Client/ClientService.php
index 8df3d3ed193bc..385a49f5a60ae 100644
--- a/lib/private/Http/Client/ClientService.php
+++ b/lib/private/Http/Client/ClientService.php
@@ -41,9 +41,9 @@ public function __construct(
 	}
 
 	#[\Override]
-	public function newClient(): IClient {
-		$handler = new CurlHandler();
-		$stack = HandlerStack::create($handler);
+	public function newClient(?callable $handler = null): IClient {
+		$clientHandler = $handler ?? new CurlHandler();
+		$stack = HandlerStack::create($clientHandler);
 		if ($this->config->getSystemValueBool('dns_pinning', true)) {
 			$stack->push($this->dnsPinMiddleware->addDnsPinning());
 		}
diff --git a/lib/public/Http/Client/IClientService.php b/lib/public/Http/Client/IClientService.php
index 12edf3dcf840e..7c853dbbe90a7 100644
--- a/lib/public/Http/Client/IClientService.php
+++ b/lib/public/Http/Client/IClientService.php
@@ -16,8 +16,10 @@
  */
 interface IClientService {
 	/**
+	 * @param ?callable $handler Handler that overrides the default CurlHandler
 	 * @return IClient
 	 * @since 8.1.0
+	 * @since 35.0.0 Added $handler optional param
 	 */
-	public function newClient(): IClient;
+	public function newClient(?callable $handler = null): IClient;
 }