Redeem Steam key to account with Steam OpenID like Humble Bundle

Humble Bundle has started requiring the user to sign in through Steam's OpenID authentication where it then redeems the Steam key on the user's account. I was unable to find any documentation on this

How to Redeem a Gifted Bundle or Game – Humble Bundle

Steam (service), Ultimate Pop Culture Wiki

Does Humble Bundle give Steam keys & how to redeem them

Does Humble Bundle give Steam keys & how to redeem them

How to Buy a Humble Bundle and Redeem It on Steam

How to Buy a Humble Bundle and Redeem It on Steam

Steam (service) - Wikipedia

How to Buy a Humble Bundle and Redeem It on Steam

Steam Key Redemption – Humble Bundle

PSA] Humble Bundle ran out of Steam keys for Back 4 Blood : r

I was previously trade banned on Steam. I made another account

Does Humble Bundle give Steam keys & how to redeem them

How to Buy a Humble Bundle and Redeem It on Steam

Email Marketing Handbook: Second Edition - IMN Inc.

Steam User Code