Fix secret key inconsistency cross the RAGFlow servers (#14591)

### What problem does this PR solve?

A and B, two API servers and a REDIS server.
If A and REDIS restart, B will hold the obsolete secret key and will
lead to error.

TODO:
app.config['SECRET_KEY'] and app.secret_key still hold obsolete secret
key.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

common/settings.py

@@ -17,6 +17,8 @@ import os
 import json
 import secrets
 import logging
+from datetime import date
+
 from common.constants import RAG_FLOW_SERVICE_NAME
 from common.file_utils import get_project_base_directory
 from common.config_utils import get_base_config, decrypt_database_config
@@ -139,6 +141,24 @@ def get_svr_queue_name(priority: int) -> str:
 def get_svr_queue_names():
     return [get_svr_queue_name(priority) for priority in [1, 0]]
 
+def init_secret_key():
+    secret_key = os.environ.get("RAGFLOW_SECRET_KEY")
+    if secret_key and len(secret_key) >= 32:
+        return secret_key
+
+    # Check if there's a configured secret key
+    configured_key = get_base_config(RAG_FLOW_SERVICE_NAME, {}).get("secret_key")
+    if configured_key and configured_key != str(date.today()) and len(configured_key) >= 32:
+        return configured_key
+    return None
+
+
+def get_secret_key():
+    global SECRET_KEY
+    if SECRET_KEY is None:
+        return _get_or_create_secret_key()
+    return SECRET_KEY
+
 def _get_or_create_secret_key():
     # secret_key = os.environ.get("RAGFLOW_SECRET_KEY")
     # if secret_key and len(secret_key) >= 32:
@@ -245,7 +265,7 @@ def init_settings():
     HOST_PORT = get_base_config(RAG_FLOW_SERVICE_NAME, {}).get("http_port")
 
     global SECRET_KEY
-    SECRET_KEY = _get_or_create_secret_key()
+    SECRET_KEY = init_secret_key()
 
 
     # authentication