feat: [torrust#424] remove secrets from settings API endpoint

These fields:

- data.tracker.token
- data.mail.password
- data.auth.secret_key

are replaced with asterisks.

src/config.rs

@@ -389,6 +389,12 @@ impl TorrustIndex {
     fn override_tracker_api_token(&mut self, tracker_api_token: &str) {
         self.tracker.override_tracker_api_token(tracker_api_token);
     }
+
+    pub fn remove_secrets(&mut self) {
+        self.tracker.token = "***".to_owned();
+        self.mail.password = "***".to_owned();
+        self.auth.secret_key = "***".to_owned();
+    }
 }
 
 /// The configuration service.

src/services/settings.rs

@@ -34,7 +34,11 @@ impl Service {
             return Err(ServiceError::Unauthorized);
         }
 
-        Ok(self.configuration.get_all().await)
+        let mut torrust_index_configuration = self.configuration.get_all().await;
+
+        torrust_index_configuration.remove_secrets();
+
+        Ok(torrust_index_configuration)
     }
 
     /// It gets only the public settings.