def verify(content, signature)
      hmac = OpenSSL::HMAC.hexdigest('sha1', @secret, content)
      signature.downcase == "sha1=#{hmac}"
    end
def verify(content, signature)
      hmac = OpenSSL::HMAC.hexdigest('sha1', @secret, content)
      signature.downcase == "sha1=#{hmac}"
    end
Verify that the feed contents were meant for this subscription
 @param [String] content
 @param [String] signature
 @return [Boolean]