Is there any way to pass a Global variables on a route?

Grafana Plugin Development
1

the json below is a part of my plugin.json, I created a route and would like to pass through the header the user who is logged in. I tried to pass a global variable but the grafana can not parse the template. is there a way to do this?

    {
    "routes": [
        {
          "path": "myapi",
          "url": "{{ .JsonData.apiUrl }}",
          "headers": [
            {
              "name": "x-grafana-user",
              "content": "{{${__user.login}}}"  // <--- it doesn't work
            }
          ],
          "tokenAuth": {
            "url": "{{ .JsonData.cognitoUrl }}",
            "params": {
              "grant_type": "client_credentials",
              "client_id": "{{ .JsonData.clientId }}",
              "client_secret": "{{ .SecureJsonData.clientSecret }}",
              "scope": "grafana_api/users"
            }
          }
        }
    }