Store and read extra user credentials with Shotgrid

Hi all,
I am currently building a custom Publish Tool in SG Desktop and the plan is for vendors to upload data to our S3 storage.
Is there a way to store the S3 credentials/keys on a per-vendor basis in Shotgrid? It’s ok for the vendor to see their own credentials even though it would be great if I could hide the keys and just pull them for the upload via the Shotgrid api.
I hope this makes sense.

Cheers,
Tobi

Store them in 2 custom fields on the HumanUser entity?

Thank you Ricardo,
That would be my first idea as well but I’m not if this is safe.
Do you know if it’s possible to hide the field for other users on the “People” page or if it’s possible to create “password-type” fields?

-Tobi