module JWT::Algos::Rsa

def sign(to_sign)
  algorithm, msg, key = to_sign.values
  raise EncodeError, "The given key is a #{key.class}. It has to be an OpenSSL::PKey::RSA instance." if key.class == String
  key.sign(OpenSSL::Digest.new(algorithm.sub('RS', 'sha')), msg)
end