check_auth_args

# File lib/net/smtp.rb, line 561
    def check_auth_args( user, secret, authtype )
      raise ArgumentError, 'both user and secret are required'\
                      unless user and secret
      auth_method = "auth_#{authtype || 'cram_md5'}"
      raise ArgumentError, "wrong auth type #{authtype}"\
                      unless respond_to?(auth_method, true)
    end