The X-Forwarded-Proto request header helps you identify the protocol (HTTP or HTTPS) that a client used to connect to your load balancer. Your server access logs contain only the protocol used between the server and the load balancer; they contain no information about the protocol used between the client and the load balancer.

http {
    map $http_x_forwarded_proto $original_scheme {
      "" $scheme;
      default $http_x_forwarded_proto;
    }
}