How to pass variables from Azure Pipeline to JavaScript?

Question

I'm attempting to run an Azure Pipeline, with some environment variables defined in the pipeline itself, and I am using the Maven Build task to build my project with Maven to launch various tests. A JS file automatically runs before each test, and I'm supposed to configure these variables in this file, which would make them available to use in the tests themselves. Currently, I have something like this:

# azure-pipelines.yml

trigger:
- none

pool:
  vmImage: ubuntu-latest

variables:
- name: user_secret
  value: "foo"

steps:

 - task: Maven@3
   inputs:
     mavenPomFile: 'pom.xml'
     goals: test
     publishJUnitResults: true
     testResultsFiles: '**/surefire-reports/TEST-*.xml'
     javaHomeOption: 'JDKVersion'
     mavenVersionOption: 'Default'
     mavenAuthenticateFeed: false
     effectivePomSkip: false
     sonarQubeRunAnalysis: false

// config.js

function fn(){
    return  {
        secret: user_secret
    };
}

The error I get is "user_secret" is not defined

I am being told I can debug it locally because the pipeline is providing the values as environment variables, and that I should be able to validate that locally by setting the variables when I run my code. Unfortunately, I can't figure out how to do it.

Similar to the above example, I also tried to get the variable process.env.user_secret, but this didn't work for me either.

How can I access Azure variables in my code?