http_secure_link not working. What is the reason?

Question

Nginx

I'm trying to set up http_secure_link. The most simplified test:

location ~ \.mp4$ {
            
            secure_link $arg_md5,$arg_expires;
            secure_link_md5 "test";

            if ($secure_link = "") { return 403; }
            if ($secure_link = "0") { return 410; }

            mp4;
            mp4_buffer_size 1m;
            mp4_max_buffer_size 5m;
        }

function buildSecureLink($url)
{
    $ttl = 10000;    
    $expires = time() + $ttl;
    $md5 = md5("test", true);
    $md5 = base64_encode($md5);
    $md5 = strtr($md5, '+/', '-_');
    $md5 = str_replace('=', '', $md5);
    
    if(strpos($url, '?') !== false)
    {
    	return $url . '&md5=' . $md5 . '&expires=' . $expires;
    }

    return $url . '?md5=' . $md5 . '&expires=' . $expires;
}

returns a 403 response. I come to the conclusion that php and nginx create different md5. What is the reason? I request

echo -n 'test' |     openssl md5 -binary | openssl base64 | tr +/ -_ | tr -d =

And I get the same hash that is contained in the url. The code matches and should work correctly
1. Why doesn't it work?
2. How can I debug?
3. Is there a way to see the real value of the hash parameter against which the get parameter is being compared?