class JWT::Decode

def verify_algo
  raise JWT::IncorrectAlgorithm, 'An algorithm must be specified' if allowed_algorithms.empty?
  raise JWT::DecodeError, 'Token header not a JSON object' unless token.header.is_a?(Hash)
  raise JWT::IncorrectAlgorithm, 'Token is missing alg header' unless alg_in_header
  raise JWT::IncorrectAlgorithm, 'Expected a different algorithm' if allowed_and_valid_algorithms.empty?
end