Obtaining Token from Frontend for Slack App (Node.js)

Question

I have developed a Next.js application that communicates with a Java Spring Boot backend using JWT tokens for authentication. Additionally, I have implemented a Slack Bolt (Node.js) application for certain features. Now, I want to fetch data from my Java backend API when users navigate to the home page in the Slack app and display it on the Slack app's home page. However, I'm concerned about securely obtaining and storing the JWT token from the frontend. How can I achieve this securely, and how should I handle token expiration effectively?