chromium/chromeos/components/test/data/onc/wifi_with_check_captive_portal.onc

{
    "GUID": "guid test",
    "IPAddressConfigType": "DHCP",
    "Name": "WiFi with check captive portal",
    "Type": "WiFi",
    "WiFi": {
        "AutoConnect": true,
        "HexSSID": "576966695769746844484350",
        "Passphrase": "some passphrase",
        "Security": "WPA-PSK"
    },
    "CheckCaptivePortal": "False"
}