How to store API keys in zoho?

How to store API keys in zoho?

Hi everyone,

I'm currently building an integration using Zoho Flow and I need to securely store several API keys that will be used to make external service calls from my flows. 
I would not like to hardcode the values in the code of custom function.

What's the recommended way to store API keys and allow access from Flow? 
Any best practices or examples from your experience would be incredibly helpful.