Add introducers

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

src/types/husk_context.rs

@@ -14,10 +14,13 @@ use sequoia_directories::Home;
 use crate::{config::HuskConfig, crypto};
 use crate::types::mail_context::MailContext;
 
+use crate::types::introducer::Introducer;
+
 pub struct HuskContext<'hc> {
     pub policy: StandardPolicy<'hc>,
     pub cert_store: CertStore<'hc>,
     pub local_trust_root: Cert,
+    pub introducers: Vec<Introducer>,
     pub mail: MailContext<'hc>,
 }
 
@@ -33,11 +36,13 @@ impl<'hc> HuskContext<'hc> {
         let policy = StandardPolicy::new();
 
         let local_trust_root = crypto::get_local_trust_root(&cert_store)?;
+        let introducers = crypto::get_introducers(&cert_store, &policy, local_trust_root.fingerprint());
 
         Ok(HuskContext {
             policy,
             cert_store,
             local_trust_root,
+            introducers,
             mail: MailContext::new(),
         })
     }

src/types/introducer.rs

@@ -0,0 +1,33 @@
+//
+// husk-milter
+//
+// introducers
+//
+
+use sequoia_wot as wot;
+use wot::{CertSynopsis, Certification};
+use sequoia_openpgp::{policy::StandardPolicy, Cert, KeyID};
+
+#[derive(Debug, Clone)]
+pub struct Introducer {
+    pub cert: CertSynopsis,
+    pub certification: Certification,
+}
+
+impl Introducer {
+
+    pub fn can_introduce(&self, email: &str) -> bool {
+        if let Some(regexset) = self.certification.regular_expressions() {
+            if regexset.matches_everything() {
+                // return false, because unlimited certifications are 
+                // ignored.
+                false
+            } else {
+                regexset.is_match(email)
+            }
+        } else {
+            false
+        }
+    }
+}
+

src/types/mod.rs

@@ -2,3 +2,4 @@ pub mod husk_context;
 pub mod mail_context;
 pub mod errors;
 pub mod recipient;
+pub mod introducer;