Fix `auth_method` not being provided to the extended auth plugin event.

Closes #1975. Thanks to Jinming Chen.

ChangeLog.txt

@@ -1,3 +1,8 @@
+Broker:
+- Fix `auth_method` not being provided to the extended auth plugin event.
+  Closes #1975.
+
+
 2.0.4 - 2020-12-22
 ==================
 

include/mosquitto_broker.h

@@ -117,7 +117,8 @@ struct mosquitto_evt_extended_auth {
 	void *data_out;
 	uint16_t data_in_len;
 	uint16_t data_out_len;
-	void *future2[4];
+	const char *auth_method;
+	void *future2[3];
 };
 
 /* Data for the MOSQ_EVT_CONTROL event */

src/security.c

@@ -936,6 +936,7 @@ int mosquitto_security_auth_start(struct mosquitto *context, bool reauth, const
 	DL_FOREACH(opts->plugin_callbacks.ext_auth_start, cb_base){
 		memset(&event_data, 0, sizeof(event_data));
 		event_data.client = context;
+		event_data.auth_method = context->auth_method;
 		event_data.data_in = data_in;
 		event_data.data_out = NULL;
 		event_data.data_in_len = data_in_len;