Firebase Hosting redirect www.site.com to site.com

I have completed my site setup via Firebase hosting, and everything works correctly. The problem is that my site make a redirect from www.site.com to site.com

How can I prevent it? How can I get always www.site.com/?

This is my firebase.json :

"hosting": {
"public": "files",
"ignore": [
  "firebase.json",
  "**/.*"
],
"headers": [ {
  "source" : "**/*.@(jpg|jpeg|gif|png)",
  "headers" : [ {
    "key" : "Cache-Control",
    "value" : "max-age=7200"
  }]
  }],
"cleanUrls": true }

Thank you in advance

Luca