Magento variable for access token

currently I have hardcoded my API token in my controller, Need to make it configurable so that it can be configured when the code is deployed in production.

So how can I store it on Magento variable from Magento cloud environment?

I see the variables section in configure environment in

If I set my customer variable there, then how can I access it in my controller file.

And what’s with so many variables types in Magento and which should i use.