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Obtain merchant_id, public_key, and private_key from Braintree (additional notes on this below)
Choose to process with Braintree native 3DS using the secure3DS box. 3DS requires the checkout page to support standard redirect handling.
Check the storeInVaultOnSuccess box if you need one-click upsells or recurring billing on this gateway. This enabled the customer vault at Braintree.
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