@Override
  public String listSessionIds() {
    StringBuilder builder = new StringBuilder();
    Iterator<String> sessionIds = getSessionCache().keySet().iterator();
    while (sessionIds.hasNext()) {
      builder.append(sessionIds.next());
      if (sessionIds.hasNext()) {
        builder.append(" ");
      }
    }
    return builder.toString();
  }
For debugging: return a list of all session ids currently active
extensions/geode-modules/src/main/java/org/apache/geode/modules/session/catalina/DeltaSessionManager.java