a failed attempt at a method that validates dwolla signatures

bad_dwolla_sig_validator.rb

# This is a failed attempt to validate the signuature Dwolla passes back with 
# a payment as described under *Dwolla's Signature on this page: 
# https://developers.dwolla.com/dev/pages/button#configuration

Class Foo
  def self.valid_dwolla_signature?(proposed_signature, checkout_id, amount)

    require 'base64'
    require 'openssl'

    dwolla_secret = Figaro.env.dwolla_secret # our secret key
    raw = "#{checkout_id}&#{amount}"
    digest  = OpenSSL::Digest::Digest.new('sha1')
    #signature = OpenSSL::HMAC.digest(digest, dwolla_secret, raw)
    signature = OpenSSL::HMAC.hexdigest(digest, dwolla_secret, raw)
    # this ALWAYS generates the wrong signature
    return (signature == proposed_signature)
  end
end