PHP - Soapclient - Basic Auth -> SERVER->REMOTE_USER

Question

We use a PHP Soap-Webservice on a 1und1-Server.
If i call the Service like

$client = new SoapClient('https://server.com/test.wsdl',
array('login'    => "tuser",
    'password' => "tpass",
    'trace' => 1)
);

all works fine and in my Server the $_SERVER['REMOTE_USER'] is set.

Now our company wants to transfer the service to a server on Microsoft Azure.
On this Server the code doesn't work the same way. The Basic auth works but there is no $_SERVER['REMOTE-USER'] variable set in my service. If i check the $_SERVER at all, there are nor vars with my login-user.

How can I fix this?