code: function loginTo (endpoint, config) {
    return global.IS_BROWSER
      ? loginFromBrowser(endpoint, config)
      : loginFromNode(endpoint, config)
  }
docs: Logs in to the specified endpoint with the given configuration
  @param {AUTH_ENDPOINTS} endpoint - the endpoint type
  @param {@link module:config-default} config - the config object
  @returns {(Promise<String>|Promise<null>)} the WebID as a string if the
  client cert is recognized, otherwise null.