title: How to send notification to specific users with FCM?
body: <p>I prepared the receiver for FCM and can send a notification to all devices. </p>
  
  <p><strong>gcm-http.googleapis.com/gcm/send</strong> with this link can send to target users who is registered and post to the target devices like below json : </p>
  
  <pre><code> {
       "notification": {
                  "title": "sample Title",
                  "text": "sample text"   },   
          "to" : "[registration id]"
           }
  </code></pre>
  
  <p>However, I need to send notifications to target users which I choose,
  via email or name...etc .
  For example: </p>
  
  <pre><code>{
       "notification": {
                  "title": "sample Title",
                  "text": "sample text"   },   
          "to" : "[email or name or sex ...]"
           }
  </code></pre>
  
  <p>How can I do that? 
  Do I need to create a web server or something else?</p>