_fetchServiceAccountToken () {
    if (!this._serviceAccountToken) {
      const fs = require('fs')
      this._serviceAccountToken = fs.readFileSync('/var/run/secrets/kubernetes.io/serviceaccount/token', 'utf8')
    }
    return this._serviceAccountToken
  }
Fetch Kubernetes service account token.
@returns {string} String representing the token of the service account running this pod.