Add introducers

- add the `Introducer` types
- get introducers from the certificate store (and log them)

src/daemon/mod.rs

@@ -93,6 +93,7 @@ impl Daemon {
         // setup Context
         match HuskContext::new(&config) {
             Ok(context) => {
+                log::debug!("found introducers: {:?}", context.introducers);
                 cx.data = Some(context).take();
                 Status::Continue
             },
@@ -149,10 +150,18 @@ impl Daemon {
         }
     }
 
-    async fn handle_data(_cx: &mut Context<HuskContext<'_>>) -> Status {
+    async fn handle_data(cx: &mut Context<HuskContext<'_>>) -> Status {
         log::debug!("DATA");
 
-        Status::Continue
+        if let Some(ref mut context) = cx.data {
+            // XXX: check for early accepting
+            // if there are no recipients with authenticated certificates
+            // tell the MTA that this milter is done and the mail can be further
+            // processed.
+            Status::Continue
+        } else {
+            Status::Tempfail
+        }
     }
 
     async fn handle_header(_cx: &mut Context<HuskContext<'_>>, name: CString, value: CString) -> Status {