fix: make external_auth pub in ConnectionSettings struct (#879)

Author: silvestrpredko

rumqttd/CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - record client id for remote link's span
 - session present flag in connack
 - Make write method return the number of bytes written correctly everywhere
+- `ConnectionSettings` can be manually created
 
 ### Security
 - Implement constant-time password comparison in authentication logic

rumqttd/src/lib.rs

@@ -149,7 +149,7 @@ pub struct ConnectionSettings {
     pub max_inflight_count: usize,
     pub auth: Option<HashMap<String, String>>,
     #[serde(skip)]
-    external_auth: Option<AuthHandler>,
+    pub external_auth: Option<AuthHandler>,
     #[serde(default)]
     pub dynamic_filters: bool,
 }