def sign(post_body)
      custom_escape(Base64.strict_encode64(OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, @secret_key, post_body)))
    end
def sign(post_body)
      custom_escape(Base64.strict_encode64(OpenSSL::HMAC.digest(OpenSSL::Digest::SHA256.new, @secret_key, post_body)))
    end
This method signs the post body that is being sent
 using the secret key provided.