Create AuthTokenCreator and AuthTokenDecryptor classes

lib/auth_token/auth_token_decryptor.rb

@@ -0,0 +1,43 @@
+class AuthTokenDecryptor
+  attr_reader :decrypted_data
+  attr_reader :token
+  attr_reader :key
+  attr_reader :user
+
+  def self.create_with_defaults(token)
+    self.new(token, Rails.application.config.secret_key_base)
+  end
+
+  def initialize(token, key)
+    @token = token
+    @key = key
+  end
+
+  def decrypt_token
+    decipher = OpenSSL::Cipher::AES.new(256, :CBC)
+    decipher.decrypt
+    decipher.key = key
+
+    base64_decoded = Base64.decode64(token)
+    plain = decipher.update(base64_decoded) + decipher.final
+
+    @decrypted_data = JSON.parse(plain, symbolize_names: true)
+  rescue OpenSSL::Cipher::CipherError
+    false
+  end
+
+  def valid?
+    decrypted_data && valid_user? && still_valid?
+  end
+
+  private
+
+  def valid_user?
+    @user = RegistrantUser.find_by(registrant_ident: decrypted_data[:user_ident])
+    @user&.username == decrypted_data[:user_username]
+  end
+
+  def still_valid?
+    decrypted_data[:expires_at] > Time.now
+  end
+end