file_get_contents, then how to use the contents?

Hello,
I've a request that looks about like this:

        $request_url1 = "http://api.ddddddd.com/http/auth?api_id=$ddd_appid&user=$ddd_user&password=$ddd_passw";
        $request_sessionid = file_get_contents($request_url1);

Code (markup):

Back from that I should get an ID I need to include in another request, if I write the address in a normal browser the response looks like this:

OK: 464fhjolilw8ad6awde8844

Code (markup):

So when I make the request to http://api.ddddddd.com/http/auth?api_id=$ddd_appid&user=$ddd_user&password=$ddd_passw I need to assign the ID I get back (464fhjolilw8ad6awde8844 in this case) to a variable so I can use it in another request, but I can't figure out how to do that so I need help...

/Oskar

 

$sess_id = str_replace('OK: ','',$request_sessionid);

Code (markup):

?