nginx_mruby で Validating payloads from GitHub (https://developer.github.com/webhooks/securing/#validating-payloads-from-github) を実装してみた。

nginx.conf

#user  nobody;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;
error_log /dev/stdout info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}

env SECRET_TOKEN;

http {
    include       mime.types;
    default_type  application/octet-stream;

    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
    #                  '$status $body_bytes_sent "$http_referer" '
    #                  '"$http_user_agent" "$http_x_forwarded_for"';

    #access_log  logs/access.log  main;
    access_log  /dev/stdout;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    #gzip  on;

    mruby_init_code '
      def hmac_secure_compare(a, b)
        ## see Rack::Utils.secure_compare
        return false unless a.bytesize == b.bytesize
        l = a.unpack("C*")
        r, i = 0, -1
        b.each_byte { |v| r |= v ^ l[i+=1] }
        r == 0
      end
    ';

    upstream app {
        server 127.0.0.1:8080;
    }

    server {
        listen       80;
        server_name  localhost;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        #location / {
        #    root   html;
        #    index  index.html index.htm;
        #}

        location / {
            mruby_access_handler_code '
              r = Nginx::Request.new
              begin
                Nginx.errlogger Nginx::LOG_ERR, "r.body: #{r.body} / X-Hub-Signature: #{r.headers_in[%q!X-Hub-Signature!]}"
                signature = "sha1=" + Digest::HMAC.hexdigest(r.body, ENV["SECRET_TOKEN"], Digest::SHA1)
                if hmac_secure_compare(signature, r.headers_in["X-Hub-Signature"])
                  Nginx.return Nginx::DECLINED
                else
                  Nginx.errlogger Nginx::LOG_ERR, "signature missmatch, Digest::HMAC.hexdigest(r.body, ...) = #{signature}"
                  Nginx.return Nginx::HTTP_FORBIDDEN
                end
              rescue => e
                Nginx.errlogger Nginx::LOG_ERR, "e: #{e.inspect}"
                Nginx.return Nginx::HTTP_FORBIDDEN
              end
            ';
            #mruby_content_handler_code '
            #  r = Nginx::Request.new
            #  Nginx.echo "server ip: #{Nginx::Connection.new.local_ip}: hello ngx_mruby world."
            #  Nginx.echo "body: #{r.body.inspect}"
            #  Nginx.echo system(r.body)
            #';
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header Host $http_host;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_pass http://app;
        }

        #error_page  404              /404.html;

        # redirect server error pages to the static page /50x.html
        #
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }

        # proxy the PHP scripts to Apache listening on 127.0.0.1:80
        #
        #location ~ \.php$ {
        #    proxy_pass   http://127.0.0.1;
        #}

        # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
        #
        #location ~ \.php$ {
        #    root           html;
        #    fastcgi_pass   127.0.0.1:9000;
        #    fastcgi_index  index.php;
        #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
        #    include        fastcgi_params;
        #}

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #
        #location ~ /\.ht {
        #    deny  all;
        #}
    }


    # another virtual host using mix of IP-, name-, and port-based configuration
    #
    #server {
    #    listen       8000;
    #    listen       somename:8080;
    #    server_name  somename  alias  another.alias;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}


    # HTTPS server
    #
    #server {
    #    listen       443 ssl;
    #    server_name  localhost;

    #    ssl_certificate      cert.pem;
    #    ssl_certificate_key  cert.key;

    #    ssl_session_cache    shared:SSL:1m;
    #    ssl_session_timeout  5m;

    #    ssl_ciphers  HIGH:!aNULL:!MD5;
    #    ssl_prefer_server_ciphers  on;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}

}

実行例.md

nginx 起動

% sudo sh -c "SECRET_TOKEN=secret /path/to/ngx_mruby/build/nginx/sbin/nginx -g 'daemon off;'"

適当なアプリを起動

Github webhook からの POST リクエストを nginx でリバースプロキシしてもらって何かするアプリ。 今回はリクエストのbodyを表示するだけ。

% ruby -rwebrick -e '
srv = WEBrick::HTTPServer.new(Port:8080);
srv.mount_proc("/"){|req, res|
   p req.body;
   #system(req.body) 
};
Signal.trap(:INT){ srv.shutdown };
srv.start
'

クライアントでHMACを計算

% ruby -ropenssl -e 'puts OpenSSL::HMAC.hexdigest(OpenSSL::Digest::SHA1.new, ARGV[0], ARGV[1])' secret asdfjkl
c2b10632589833129d6825e3fd349b0061501e62

クライアントからリクエスト送信

% curl -H 'X-Hub-Signature: sha1=c2b10632589833129d6825e3fd349b0061501e62' -d 'asdfjkl' -v http://127.0.0.1/