8.5.5 to 8.5.6 -> SOAP requests now with 401 errors after upgrade

[brainfoolong]

Description

Our CI tests fail with 8.5.6 and works with 8.5.5 when doing SOAP requests.

I cannot share exact details for server and credentials, but we are working with Exchange EWS API.

After upgrading from 8.5.5 to 8.5.6 our SOAP code errors out with "401" unauthorized.

Reverting back to 8.5.5 and everything work fine.

I can't see any related change in the changelog for 8.5.6 that may affect this, are there any changes that i need to know or settings i need to change? For now, i cannot get it to work with 8.5.6

The soap client is initialized with this values

new SoapClient(
            dirname(__FILE__) . '/assets/services.wsdl',
            array(
                'user' => $this->username,
                'password' => $this->password,
                'location' => 'https://' . $this->server . '/EWS/Exchange.asmx',
                'classmap' => $this->classMap(),
                'curlopts' => $this->curl_options,
                'features' => SOAP_SINGLE_ELEMENT_ARRAYS,
            )
        );

The error response with 8.5.6 is

["__last_response_headers":protected]=>
  string(291) "HTTP/1.1 401 Unauthorized
Server: Microsoft-IIS/10.0
...

With 8.5.5 we get, without any code change

["__last_response_headers":protected]=>
  string(291) "HTTP/1.1 200
Server: Microsoft-IIS/10.0
...

PHP Version

Error Version:
PHP 8.5.6 (cli) (built: May 18 2026 17:15:53) (ZTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Zend Engine v4.5.6, Copyright (c) Zend Technologies
    with Xdebug v3.6.0-dev, Copyright (c) 2002-2025, by Derick Rethans
    with Zend OPcache v8.5.6, Copyright (c), by Zend Technologies

Working Version:
PHP 8.5.5 (cli) (built: Apr 10 2026 18:39:23) (ZTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Zend Engine v4.5.5, Copyright (c) Zend Technologies
    with Xdebug v3.6.0-dev, Copyright (c) 2002-2025, by Derick Rethans
    with Zend OPcache v8.5.5, Copyright (c), by Zend Technologies

Operating System

Windows