class Doorkeeper::OAuth::AuthorizationCodeRequest

def validate_code_verifier
  return true unless grant.uses_pkce? || code_verifier
  return false unless grant.pkce_supported?
  if grant.code_challenge_method == "S256"
    grant.code_challenge == AccessGrant.generate_code_challenge(code_verifier)
  elsif grant.code_challenge_method == "plain"
    grant.code_challenge == code_verifier
  else
    false
  end
end