Don't mutate WebhooksHelper parameters

lib/square/utilities/webhooks_helper.rb

@@ -8,12 +8,11 @@ def self.is_valid_webhook_event_signature(request_body, signature_header, signat
       raise 'signature_key is null or empty' if signature_key.nil? || signature_key.empty?
       raise 'notification_url is null or empty' if notification_url.nil? || notification_url.empty?
 
-      # Perform UTF-8 encoding to bytes
-      payload_bytes = "#{notification_url}#{request_body}".force_encoding('utf-8')
-      signature_key_bytes = signature_key.force_encoding('utf-8')
+      # Prepare the message as it was signed by the sender
+      message = "#{notification_url}#{request_body}"
 
       # Compute the hash value
-      hmac = OpenSSL::HMAC.digest('sha256', signature_key_bytes, payload_bytes)
+      hmac = OpenSSL::HMAC.digest('sha256', signature_key, message)
 
       # Compare the computed hash vs the value in the signature header
       hash_base64 = Base64.strict_encode64(hmac)

test/webhooks/test_webhooks_helper.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../lib/square/utilities/webhooks_helper.rb'
 require 'minitest/autorun'
 require 'minitest/hell'