How to get Auth Token of an account using custom function or Zoho API?

How to get Auth Token of an account using custom function or Zoho API?

Hi, 

I am working on creation of a Zoho Extension using Zoho Platform. 
Here, I need auth-token of account on which our extension will be installed. 

So I need to get auth-token dynamically, means I need to get auth-token of the account using custom function/Deluge script or Zoho API.

Is it possible to do this?
Please tell me.

Thanks