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

G2A sold $450k worth of our game keys : r/Games

7 Sites for Cheap Steam Keys Like Humble Bundle

Free Game Redemption Instructions – Humble Bundle

Steam (service), Ultimate Pop Culture Wiki

How to Buy a Humble Bundle and Redeem It on Steam

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I randomly got this message today for a game I got in a Humble

Do you have to redeem humble bundle keys on the steam account that

How to Buy a Humble Bundle and Redeem It on Steam

13 simple ways to redeem Steam Games automatically (I made a