in src/main/java/com/googlesource/gerrit/plugins/gitblit/auth/GerritAuthFilter.java [53:70]
  public UserModel getUser(HttpServletRequest httpRequest) {
    UserModel user = null;
    String username = (String) httpRequest.getAttribute("gerrit-username");
    String token = (String) httpRequest.getAttribute("gerrit-token");
    if (token == null || username == null) {
      return null;
    }
    user =
        gitBlit.authenticate(
            username, (GerritToGitBlitUserService.SESSIONAUTH + token).toCharArray(), null);
    if (user != null) {
      return user;
    }
    return null;
  }