如何从 URL 中提取 “?referer=” 和 “&username=” 之间的内容？

web.admin.com/admin/usermanage/investuser?start=2018-01-02%2000:00:00&end=2018-01-02%2010:41:46&itype=3&isfirst=3&referer=http://testhf.irongbei.com/muserregister/register2?v=10f454&key=311bcdec754052e40fe025a54f488f9a&rbref=rbzc&isshow=&username=&pname=&plattype=0&istatus=1&buy_type=0&channel_source=62

$encodedUrl = 'web.admin.com/admin/userManage/investuser?start=2018-01-02%2000:00:00&end=2018-01-02%2010:41:46&itype=3&isfirst=3&referer=http://testhf.irongbei.com/MUserRegister/register2?v=10f454&key=311bcdec754052e40fe025a54f488f9a&rbref=rbzc&isShow=&username=&pname=&plattype=0&istatus=1&buy_type=0&channel_source=62';
$decodedUrl = urldecode($encodedUrl);

preg_match('/referer=(.*?)&username/', $decodedUrl, $matches);
if (isset($matches[1])) {
    $result = $matches[1];
} else {
    $result = null;
}

echo $result; //输出 "http://testhf.irongbei.com/MUserRegister/register2?v=10f454&key=311bcdec754052e40fe025a54f488f9a&rbref=rbzc"