How to remove slash from $http_referer variable

I want to use NGINX as dynamic local CDN with proxy_pass based on Referer header and $http_refere variable. The problem is that the Referer (variable too) header contains a "/" at the end of the URL. I want to delete trailing slash in $http_referer. How can I do it?

My NGINX location:

location / {
  add_header 'Access-Control-Allow-Origin' '*';
  add_header Referrer-Policy 'strict-origin';
  proxy_pass $http_referer;
}