Validates redirect URLs to prevent open redirect vulnerabilities.

By default, only relative URLs (starting with /) are allowed. You can configure a custom validator callback in your application config:

config :keen_auth,
  redirect_validator: &MyApp.Auth.validate_redirect/2

Callback Signature

The callback receives the redirect URL and the connection, and should return:

• {:ok, url} - URL is valid, use this URL (allows transformation)
• :error - URL is invalid, will fall back to "/"

Examples

Relative paths only (default)

config :keen_auth,
  redirect_validator: &KeenAuth.Helpers.RedirectValidator.relative_only/2

Database-backed allowlist

def validate_redirect(url, _conn) do
  uri = URI.parse(url)
  if AllowedDomains.exists?(uri.host) do
    {:ok, url}
  else
    :error
  end
end

Allow specific domains

def validate_redirect(url, _conn) do
  uri = URI.parse(url)
  allowed = ["myapp.com", "app.myapp.com", nil]  # nil = relative URL
  if uri.host in allowed, do: {:ok, url}, else: :error
end