release: authorize webhook request using webhook secret token

GitHub: GH-43

In this PR, we set up the authorization flow for webhook requests.
At the following PRs, we will implement the logic of deployments.

Author: otegami

ansible/files/home/deployer/webhook/lib/deployer/app.rb

@@ -1,3 +1,4 @@
+# Copyright (C) 2024  Horimoto Yasuhiro <horimoto@clear-code.com>
 # Copyright (C) 2024  Takuya Kodama <otegami@clear-code.com>
 #
 # This program is free software: you can redistribute it and/or modify
@@ -13,10 +14,38 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+require "openssl"
+require_relative "response"
+
 module Deployer
   class App
     def call(env)
-      [200, {}, ["Hello deployer"]]
+      request = Rack::Request.new(env)
+      response = Response.new
+      process(request, response) or response.finish
+    end
+
+    private
+
+    def process(request, response)
+      unless request.post?
+        response.set(:method_not_allowed, "must POST")
+        return nil
+      end
+
+      unless verify_signature(request)
+        response.set(:unauthorized, "Authorization failed")
+        return nil
+      end
+
+      response.finish
+    end
+
+    def verify_signature(request)
+      signature = 'sha256=' + OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha256'),
+                                                      ENV['SECRET_TOKEN'],
+                                                      request.body.read)
+      Rack::Utils.secure_compare(signature, request.env['HTTP_X_HUB_SIGNATURE_256'])
     end
   end
 end

ansible/files/home/deployer/webhook/lib/deployer/response.rb

@@ -0,0 +1,27 @@
+# Copyright (C) 2010-2019  Sutou Kouhei <kou@clear-code.com>
+# Copyright (C) 2015  Kenji Okimoto <okimoto@clear-code.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+require "rack/response"
+
+module Deployer
+  class Response < Rack::Response
+    def set(status_keyword, message)
+      self.status = Rack::Utils.status_code(status_keyword)
+      self["Content-Type"] = "text/plain"
+      write(message)
+    end
+  end
+end