Nginx virtual host config for Proxmox. To hide pveproxy on 8006 port behind. With working VNC passthrough.

nginx-vhost-proxprox.conf

###
# Nginx vhost file to hide Proxmox pveproxy
# For 3.4+, 5.x version.
#
# Do not forget to create file
# /etc/default/pveproxy:
# ALLOW_FROM="127.0.0.1"
# DENY_FROM="all"
# POLICY="allow"
#
# @2019-08-05
# - disable big iso/templates upload buffering
#
# @2018-08-01 - changes
# - add missing special locations for proxmoxlib.js, vnc
#
# @2017-11-17 - changes
# - use nginx-1.10+ for https
# - move proxy_params inside locations cos
#   some parameters/header are dropping to defaults by the way
# - add other hacks to skip proxy to pveproxy: docs
# - add special location for api access
# - add some descriptions to options

server {
        # nginx-1.0+
        #listen 443 ssl;
        # nginx-1.6+
        #listen 443 ssl spdy;
        # nginx-1.10+
        listen 443 ssl http2;

        root    /var/www/default;

        # Set YOUR server name here
        server_name proxmox.example.com;

        # Check for cross-framing - nuke bustards
        valid_referers none blocked server_names;
        if ($invalid_referer) {
            return 403;
        }
        # Hint for browsers
        add_header X-Frame-Options SAMEORIGIN;
        # Don't "detect" file type by extension (IE10+?)
        add_header X-Content-Type-Options nosniff;
        
        access_log /var/log/nginx/proxmox.example.com-ssl-access.log;
        error_log /var/log/nginx/proxmox.example.com-ssl-error.log;

        # load images, backups, iso...
        client_max_body_size 64m;

        include proxy_params;
        # Your certificates here must be
        include ssl/proxmox.conf;

        # restrict supported by pveproxy ssl protocols
        # Special for Proxmox-3
        proxy_ssl_protocols     TLSv1;
        # Special for Proxmox-5+
        #proxy_ssl_protocols    TLSv1.2;

        location / {
                # Magic for VNC
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "upgrade";

                include proxy_params;
                proxy_pass https://127.0.0.1:8006;
        }

        location ~* ^/(api2|novnc)/ {
                proxy_redirect off;
                # Magic for VNC
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "upgrade";

                # Upload templates/iso
                location ~* ^/api2/json/nodes/.*/storage/.*/upload {
                        client_max_body_size 2000m;
                        # nginx-1.8+
                        proxy_request_buffering off;
                        proxy_max_temp_file_size 0;

                        include proxy_params;
                        proxy_pass https://127.0.0.1:8006;
                }

                include proxy_params;
                proxy_pass https://127.0.0.1:8006;
        }

        # MAGICK !!!
        # Proxmox Web-UI loads DEBUG version of ExtJS
        # And nginx waaaaaing sooo long. And hangs.
        # Do not proxy static files, just give them
        location ~* ^/pve2/(?<file>.*)$ {
                gzip_static on;
                root /usr/share/pve-manager;
                try_files /$file @proxmox;
        }
        # Special for proxmox-5.x
        location ~* ^/proxmox.*\.js$ {
                gzip_static on;
                root /usr/share/usr/share/javascript/proxmox-widget-toolkit;
                try_files $uri @proxmox;
        }
        location ~* ^/pve-docs/(?<file>.*)$ {
                gzip_static on;
                root /usr/share/pve-docs;
                try_files /$file @proxmox;
        }
        location @proxmox {
                internal;

                # Magic for VNC
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "upgrade";

                # nginx-1.8+
                proxy_request_buffering off;
                proxy_max_temp_file_size 0;

                include proxy_params;
                proxy_pass https://127.0.0.1:8006;
        }
}

I assume that you use these configs on proxmox host machine.

You should define ssl configs for nginx in file /etc/nginx/ssl/proxmox.conf - paths to certificate and key, cyphers.
Read about it there: https://nginx.org/en/docs/http/configuring_https_servers.html

Or disable line with include ssl/proxmox.conf. And change listen option to listen 80;. Not recommended though.

Updated gist: restrict proxy ssl protocols to supported by pveproxy.
On Proxmox-3 its limited to TLSv1.1, on Proxmox-5+ - to TLSv1.2.

Update gist: on Proxmox-3 pveproxy limited to TLSv1.