add ability to use timestamp server

lib/submissions/timestamp_handler.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module Submissions
+  class TimestampHandler
+    HASH_ALGORITHM = 'SHA512'
+
+    TimestampError = Class.new(StandardError)
+
+    attr_reader :tsa_url
+
+    def initialize(tsa_url:)
+      @tsa_url = tsa_url
+    end
+
+    def finalize_objects(_signature_field, signature)
+      signature.document.version = '2.0'
+
+      signature[:Type] = :DocTimeStamp
+      signature[:Filter] = :'Adobe.PPKLite'
+      signature[:SubFilter] = :'ETSI.RFC3161'
+    end
+
+    def sign(io, byte_range)
+      digest = OpenSSL::Digest.new(HASH_ALGORITHM)
+
+      io.pos = byte_range[0]
+      digest << io.read(byte_range[1])
+      io.pos = byte_range[2]
+      digest << io.read(byte_range[3])
+
+      uri = Addressable::URI.parse(tsa_url)
+
+      conn = Faraday.new(uri.origin) do |c|
+        c.basic_auth(uri.user, uri.password) if uri.password.present?
+      end
+
+      response = conn.post(uri.path, build_payload(digest.digest),
+                           'content-type' => 'application/timestamp-query')
+
+      raise TimestampError if response.status != 200 || response.body.blank?
+
+      OpenSSL::Timestamp::Response.new(response.body).token.to_der
+    end
+
+    def build_payload(digest)
+      req = OpenSSL::Timestamp::Request.new
+      req.algorithm = HASH_ALGORITHM
+      req.message_imprint = digest
+
+      req.to_der
+    end
+  end
+end