SSO credentials validity / forced logout

I think I’m close, using simple PHP commands. The code is below. The username choice came from this post.

I’m getting this response… does this mean anything to anyone? Seems like an SSL protocol version thing?

error:1407742E:SSL routines:SSL23_GET_SERVER_HELLO:tlsv1 alert protocol version

Here is my code:

    $url = "https://community.mysite.com/admin/users/100004/log_out";
    $headers = array( 'Api-Key' => 'd412mylongadminkeyaadcd',
    				  'Api-Username' => 'system',
    				  );

	$ch = curl_init();
	curl_setopt($ch, CURLOPT_URL, $url);

[edit: added these lines too, no change:]
	curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
	curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
[/edit]

	curl_setopt($ch, CURLOPT_POST, true);
	curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    $data = curl_exec($ch);
    if (curl_errno($ch)) {
        echo curl_error($ch);
    }
    curl_close($ch);