encoder.rb in webhook_system-2.0.0

- old
+ new
@@ -6,62 +6,117 @@
     # encrypt it, base64 encode that, and wrap it in its own json wrapper
     #
     # @param [String] secret_string some secret string
     # @param [Object#to_json] payload Any object that responds to to_json
     # @return [String] The encoded string payload (its a JSON string)
-    def self.encode(secret_string, payload)
-      cipher = OpenSSL::Cipher::AES256.new(:CBC)
-      cipher.encrypt
-      iv = cipher.random_iv
-      cipher.key = key_from_secret(iv, secret_string)
-      encoded = cipher.update(payload.to_json) + cipher.final
-      Payload.encode(encoded, iv)
+    def self.encode(secret_string, payload, format:)
+      response_hash = Payload.encode(payload, secret: secret_string, format: format)
+      payload_string = JSON.generate(response_hash)
+      signature = hub_signature(payload_string, secret_string)
+      [payload_string, { 'X-Hub-Signature' => signature, 'Content-Type' => content_type_for_format(format) }]
     end
 
     # Given a secret string, and an encrypted payload, unwrap it, bas64 decode it
     # decrypt it, and JSON decode it
     #
     # @param [String] secret_string some secret string
-    # @param [String] payload String as returned from #encode
+    # @param [String] payload_string String as returned from #encode
     # @return [Object] return the JSON decode of the encrypted payload
-    def self.decode(secret_string, payload)
-      encoded, iv = Payload.decode(payload)
-      cipher = OpenSSL::Cipher::AES256.new(:CBC)
-      cipher.decrypt
-      cipher.iv = iv
-      cipher.key = key_from_secret(iv, secret_string)
-      decoded = cipher.update(encoded) + cipher.final
-      JSON.load(decoded)
-    rescue OpenSSL::Cipher::CipherError
-      raise DecodingError, 'Decoding Failed, probably mismatched secret'
+    def self.decode(secret_string, payload_string, headers = {})
+      signature = headers['X-Hub-Signature']
+      format = format_for_content_type(headers.fetch('Content-Type'))
+
+      payload_signature = hub_signature(payload_string, secret_string)
+      if signature && signature != payload_signature
+        raise DecodingError, 'signature mismatch'
+      end
+
+      Payload.decode(payload_string, secret: secret_string, format: format)
     end
 
     class << self
       private
 
-      def key_from_secret(iv, secret_string)
-        OpenSSL::PKCS5.pbkdf2_hmac(secret_string, iv, 100_000, 256 / 8, 'SHA256')
+      def content_type_format_map
+        {
+          'base64+aes256' => 'application/json; base64+aes256',
+          'json' => 'application/json'
+        }
       end
+
+      def format_for_content_type(content_type)
+        content_type_format_map.invert.fetch(content_type)
+      end
+
+      def content_type_for_format(format)
+        content_type_format_map.fetch(format)
+      end
+
+      def hub_signature(payload_string, secret)
+        'sha1=' + OpenSSL::HMAC.hexdigest(OpenSSL::Digest.new('sha1'), secret, payload_string)
+      end
     end
   end
 
-  # private class to just wrap the outer wrapping of the response format
-  # not exposed to the outside
-  # :nodoc:
   module Payload
-    def self.encode(raw_encrypted_data, iv)
-      JSON.pretty_generate(
-        'format' => 'base64+aes256',
-        'payload' => Base64.encode64(raw_encrypted_data),
-        'iv' => Base64.encode64(iv)
-      )
-    end
+    class << self
+      def encode(payload, secret:, format:)
+        case format
+        when 'base64+aes256'
+          encode_aes(payload, secret)
+        when 'json'
+          payload
+        else
+          raise ArgumentError, "don't know how to handle: #{payload['format']} payload"
+        end
+      end
 
-    def self.decode(payload_string)
-      payload = JSON.load(payload_string)
-      unless payload['format'] == 'base64+aes256'
-        raise ArgumentError, 'only know how to handle base64+aes256 payloads'
+      def decode(response_body, secret:, format:)
+        payload = JSON.load(response_body)
+
+        case format
+        when 'base64+aes256'
+          decode_aes(payload, secret)
+        when 'json'
+          payload
+        else
+          raise ArgumentError, "don't know how to handle: #{payload['format']} payload"
+        end
       end
-      [Base64.decode64(payload['payload']), Base64.decode64(payload['iv'])]
+
+      private
+
+      def encode_aes(payload, secret)
+        cipher = OpenSSL::Cipher::AES256.new(:CBC)
+        cipher.encrypt
+        iv = cipher.random_iv
+        cipher.key = key_from_secret(iv, secret)
+        encoded = cipher.update(payload.to_json) + cipher.final
+
+        {
+          format: 'base64+aes256',
+          payload: Base64.encode64(encoded),
+          iv: Base64.encode64(iv),
+        }
+      end
+
+      def decode_aes(payload, secret)
+        encoded = Base64.decode64(payload['payload'])
+        iv = Base64.decode64(payload['iv'])
+
+        cipher = OpenSSL::Cipher::AES256.new(:CBC)
+        cipher.decrypt
+        cipher.iv = iv
+        cipher.key = key_from_secret(iv, secret)
+        decoded = cipher.update(encoded) + cipher.final
+
+        JSON.load(decoded)
+      rescue OpenSSL::Cipher::CipherError
+        raise DecodingError, 'Decoding Failed, probably mismatched secret'
+      end
+
+      def key_from_secret(iv, secret_string)
+        OpenSSL::PKCS5.pbkdf2_hmac(secret_string, iv, 100_000, 256 / 8, 'SHA256')
+      end
     end
   end
 end