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 Buy a Humble Bundle and Redeem It on Steam

Linking your Steam and Humble Bundle Accounts – Humble Bundle

Steam (service) - Wikipedia

Petition · Elder Scrolls Online Steam Keys for Existing Owners

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

Keys are Temporarily Exhausted and Delayed Delivery Errors

How to claim your Steam key : r/EliteDangerous

CustomKart/packages/MaterialDesignThemes.2.5.1/src/net45

How to Buy a Humble Bundle and Redeem It on Steam

How to Buy a Humble Bundle and Redeem It on Steam

How to Buy a Humble Bundle and Redeem It on Steam

Account got Hijacked - Please DON'T make my mistake!

Does Humble Bundle give Steam keys & how to redeem them

How to Link Your Steam Account – Humble Bundle