title: VS Code Debugging launch.json - Use `envFile` values in `env`
body: <p>When debugging some python code in VSCode I would like for developers to be able to create a simple small <code>envFile</code> that looks something like...</p>
  
  <pre><code>AD_USR=username
  AD_PSW=password
  </code></pre>
  
  <p>so those values can later be substituted into multiple other environment variables.</p>
  
  <p>I tried to do something like below (note how the <code>env</code> vars are attempting to to consume the environment variables that were set in the <code>envFile</code>).</p>
  
  <p>This does not work. </p>
  
  <pre><code>{
      "version": "0.2.0",
      "configurations": [
          {
              "name": "Debug My Program",
              "type": "python",
              "request": "launch",
              "program": "${workspaceFolder}/venv/bin/thingtorun",
              "console": "integratedTerminal",
              "envFile": "${workspaceFolder}/bin/.envFile",
              "env": {
                  "SYSTEM_A_USER": "${env.AD_USR}",
                  "SYSTEM_A_PASSWORD": "${env.AD_PSW}",
                  "SYSTEM_B_USER": "${env.AD_USR}",
                  "SYSTEM_B_PASSWORD": "${env.AD_PSW}",
                  ... + lots of other systems ...
              }
          }
      ]
  }
  </code></pre>
  
  <p>Does anyone know of a mechnism of doing this?</p>
  
  <p>My main objective is to avoid new developers having to create a huge <code>envFile</code> repeating their username and password for every system.  In prod the usernames and password will vary so I cannot eliminate the need for SYSTEM_X_USER/PASSWORD either.</p>