Looks like Southwest is pushing out a forced password update to ensure they meet a security criteria. Given that A-List Preferred members must login to receive their free WiFi perk, they are providing a temporary promo code for those who do not wish to change it on the spot.
The catch? Although this promo code is supposed to be for A-List Preferred members, ANYONE can use it without login or credentials.
Once on the plane
-- Enter in promo code "ALP-KL4" during the checkout, and it marks it down to free with no credit card or information entry necessary. This is unlimited free WiFi on Southwest while this password update phase lasts (not defined at this point).
UPDATE: "ALP-KL6" appears to be the new working code. Verify with the A-List Preferred login process if you have any issue!