class ActionDispatch::Cookies::SignedCookieJar

def ensure_secret_secure(secret)

secret they've provided is at least 30 characters in length.
To prevent users from using something insecure like "Password" we make sure that the 
def ensure_secret_secure(secret)
  if secret.blank?
    raise ArgumentError, "A secret is required to generate an " +
      "integrity hash for cookie session data. Use " +
      "config.secret_token = \"some secret phrase of at " +
      "least #{SECRET_MIN_LENGTH} characters\"" +
      "in config/initializers/secret_token.rb"
  end
  if secret.length < SECRET_MIN_LENGTH
    raise ArgumentError, "Secret should be something secure, " +
      "like \"#{ActiveSupport::SecureRandom.hex(16)}\".  The value you " +
      "provided, \"#{secret}\", is shorter than the minimum length " +
      "of #{SECRET_MIN_LENGTH} characters"
  end
end