anti-bot nginx snippet

private.conf

        location ~ ^/private/.*[.]html$ {
                try_files /$d_pelican$uri /$d_pelican$uri/index.html /_web$uri @tryredir;
                # can check $request_filename
                set $h_robots "noindex, nofollow, noarchive, nosnippet, none";
                expires 5m;
                max_ranges 0;
                header_filter_by_lua_block {
                        local pcre = require "pcre"
                        if ngx.var.http_accept_language == nil then
                                return ngx.exit(403)
                        elseif ngx.var.http_user_agent == nil then
                                return ngx.exit(403)
                        elseif ngx.var.http_accept_encoding == nil then
                                return ngx.exit(403)
                        elseif pcre.find(ngx.var.http_accept_encoding, '\\bbr\\b') == nil then
                                return ngx.exit(403)
                        else
                                local ua = ngx.var.http_user_agent
                                if pcre.find(ua, '^(Mozilla|Opera)/') == nil then
                                        return ngx.exit(403)
                                elseif pcre.find(ua, '\\bhttps?://') ~= nil then
                                        return ngx.exit(403)
                                end
                        end
                }
        }