added signature method for the secure mode

CHANGELOG.md

@@ -3,6 +3,10 @@
 ## 3.0.0 (unreleased)
 
 
+**Features:**
+
+- added helper for generating signature
+
 ## 2.3.2
 
 **Bug fixes:**

README.md

@@ -54,3 +54,8 @@ Castle.configure do |config|
   config.source_header = 'backend'
 end
 ```
+
+
+## Signature
+
+`Castle::SecureMode.signature(user_id)` will create a signed user_id.

lib/castle.rb

@@ -10,6 +10,7 @@
 require 'castle/errors'
 require 'castle/system'
 require 'castle/header_formatter'
+require 'castle/secure_mode'
 require 'castle/extractors/client_id'
 require 'castle/extractors/headers'
 require 'castle/extractors/ip'

lib/castle/secure_mode.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+require 'openssl'
+
+module Castle
+  module SecureMode
+    def self.signature(user_id)
+      OpenSSL::HMAC.hexdigest('sha256', Castle.config.api_secret, user_id.to_s)
+    end
+  end
+end

spec/lib/castle/secure_mode_spec.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Castle::SecureMode do
+  it 'has signature' do
+    expect(described_class.signature('test')).to eql(
+      '0329a06b62cd16b33eb6792be8c60b158d89a2ee3a876fce9a881ebb488c0914'
+    )
+  end
+end