chore: enhance the README for exhook-svr-python

exhook-svr-python/.gitignore

@@ -1,3 +1 @@
 __pycache__
-exhook_pb2.py
-exhook_pb2_grpc.py

exhook-svr-python/README.md

@@ -6,23 +6,108 @@ This is a demo server written in python for exhook
 
 - [Python](https://www.python.org) 3.5 or higher
 - pip version 9.0.1 or higher
+- EMQX 5.0 or higher
 
-## Run
+### Install gRPC and gRPC tools
 
-Install gRPC and gRPC Tools:
+Before running, we need to install the following dependencies related to gRPC:
 
 ```
 python -m pip install grpcio
 python -m pip install grpcio-tools
 ```
-Try to compile the `*.proto` files:
 
+## Test it with EMQX
+
+1. Make sure that EMQX is version 5.0 or above.
+
+2. Start this ExHook Demo server by the following command:
 ```
-python -m grpc_tools.protoc -I./protos --python_out=. --grpc_python_out=. ./protos/exhook.proto
+python exhook_server.py
 ```
 
-Run server:
+3. Configure ExHook by the EMQX Dashboard for this Demo server and ensure that its address points
+   to this example program.
+   For the detailed docs, refer to the
+   [Offcial Documentation](https://docs.emqx.com/en/enterprise/v5.1/extensions/exhook.html)
 
+4. Observing this example program, it will print that it has received the `OnProviderLoaded`
+   callback, indicating that they have successfully established a connection. e.g:
 ```
-python exhook_server.py
+OnProviderLoaded: broker {
+  version: "5.1.0"
+  sysdescr: "EMQX"
+  uptime: 67553173
+  datetime: "2023-07-01T02:03:24.826755959+00:00"
+}
+...
+```
+
+5. Use an MQTT client, such as [MQTTX](https://mqttx.app/), to connect to EMQX and
+   observe the output of this example program. e.g:
+
+```
+OnClientConnect: ...
+OnClientAuthenticate: ...
+OnSessionCreated: ...
+OnClientConnected: ...
+OnClientConnack: ...
+```
+
+At this point, the example program has successfully integrated with EMQX and received all client
+events from EMQX.
+
+## Modify the exhook_server.py to deny all MQTT connecting request
+
+In this section, we will take the `OnClientAuthenticate` callback as an example and attempt to
+modify its implementation in `exhook_server.py` to deny some MQTT client connections.
+
+1. Modify the `OnClientAuthenticate` function in `exhook_server.py` to reject all client logins
+   with the username "baduser".
+   The complete implementation of the modified function is as follows:
+```
+def OnClientAuthenticate(self, request, context):
+    print("OnClientAuthenticate:", request)
+    clientinfo = request.clientinfo
+    if clientinfo.username == "baduser":
+        reply = exhook_pb2.ValuedResponse(type="STOP_AND_RETURN", bool_result=False)
+    else:
+        reply = exhook_pb2.ValuedResponse(type="STOP_AND_RETURN", bool_result=True)
+    return reply
+```
+
+2. Shutdown and restart `exhook_server.py`.
+
+3. Set the username of the MQTT client to "baduser" and connect to EMQX to test.
+
+4. It can be observed that the client is unable to connect due to authentication failure, and the
+   `exhook_server.py` will also output similar logs like this:
+```
+OnClientConnect: ...
+OnClientAuthenticate: ...
+OnClientConnack: ...
+result_code: "not_authorized"
+...
+```
+
+Finally, a simple custom authentication based on ExHooK is completed.
+
+
+## Update the exhook.proto to latest version
+
+Due to the inconsistency between the exhook.proto file used in this demo and the one included
+in your installed version of EMQX, you may need to ensure their consistency.
+
+For example, in EMQX v5.1.0, this file is located at
+https://github.com/emqx/emqx/blob/v5.1.0/apps/emqx_exhook/priv/protos/exhook.proto
+
+You need to manually update it to the `protos/exproto.proto` location and
+regenerate code via the following command:
+
 ```
+python -m grpc_tools.protoc -I./protos --python_out=. --grpc_python_out=. ./protos/exhook.proto
+```
+
+## References
+
+- [gRPC.io Python Quick start](https://grpc.io/docs/languages/python/quickstart/)