Get new access_token using unirest to create a ticket Note with attachments

I’m working on a Serverless app built for platfrorm 3.1, I’m having an issue with using Freshservice Create Note API Service Desk API for Developers | Freshservice

I’ve configured OAuth to use Freshservice API for Ticket and Asset endpoints. And now I need to create a note with a list of image attachments. I’ve tried to use the Request API, but I found out that it doesn’t support HTTP requests with attachments (Creating tickets with attachments using serverless apps - #2 by kannansantharam)

So, I’ve tried using unirest which can work if I pass access_token (from OAuth2) in the authentication header. But my question is how can I get the oauth_details that are saved inside the app after OAuth process (when user grants API access to my app)? It seems like this information cannot be accessed from the app using fdk tools. All examples that I could find have unirest used with API Key, not with OAuth. What is the most appropriate way to handle this case with fdk in a serverless app using platfrorm 3.1?