def get_signature_hash(params, secret)
      Digest::MD5.hexdigest(get_signature_string(params, secret)).to_s
    end
def get_signature_hash(params, secret)
      Digest::MD5.hexdigest(get_signature_string(params, secret)).to_s
    end
params:
   params, Hash
   secret, String
 returns:
   String

 Returns an MD5 hash of the signature string for an API call.