def auth_signature(client_data_json)
      data = [
        ::U2F::DIGEST.digest(app_id),
        1, # User present
        counter,
        ::U2F::DIGEST.digest(client_data_json)
      ].pack('A32CNA32')

      origin_key.sign(::U2F::DIGEST.new, data)
    end
def auth_signature(client_data_json)
      data = [
        ::U2F::DIGEST.digest(app_id),
        1, # User present
        counter,
        ::U2F::DIGEST.digest(client_data_json)
      ].pack('A32CNA32')

      origin_key.sign(::U2F::DIGEST.new, data)
    end
The signature field of a signatureData field of a SignResponse Hash.

 client_data_json - The JSON encoded clientData String.

 Returns an ECDSA signature String.