Implement 'introducer remove'

- Implement the subcommand `remove` for `introducer`.
- Remove the introducer by adding a certification with trust level 1 and
  trust depth 0.
- Move `crypt.rs` into `common/` and add a generic authenticaton
  function to be used by `introducer add` and `... remove`.

src/types/introducer.rs

@@ -1,22 +1,15 @@
 //! introducers
 
-use std::sync::Arc;
-
 use anyhow::Result;
 
-use sequoia_cert_store::StoreUpdate;
-use sequoia_cert_store::store::MergePublicCollectStats;
-use sequoia_openpgp::packet::prelude::SignatureBuilder;
 use sequoia_wot as wot;
 use wot::{CertSynopsis, Certification};
 use sequoia_openpgp::{cert::ValidCert, policy::StandardPolicy};
 use sequoia_openpgp::Cert;
 use sequoia_openpgp::Fingerprint;
-use sequoia_openpgp::types::SignatureType;
 
-use crate::mail;
 use crate::types::husk_context::HuskContext;
-use crate::common::escape;
+use crate::common::crypto;
 
 #[derive(thiserror::Error, Debug)]
 pub enum IntroducerError {
@@ -87,86 +80,19 @@ impl Introducer {
             return Err(IntroducerError::UnsuitableCertificate.into());
         }
 
-        let policy = &context.policy;
-        let root_signing_key = match context.local_trust_root.with_policy(policy, None)?
-            .keys()
-            .supported()
-            .alive()
-            .revoked(false)
-            .for_certification()
-            .next() {
-                Some(k) => k.key(),
-                None => {
-                    return Err(IntroducerError::RootDamaged.into());
-                }
-            };
-        let mut root_signer = root_signing_key
-            .clone()
-            .parts_into_secret()?
-            .into_keypair()?;
+        crypto::authenticate(context, cert, true, Some(domains))
+    }
 
+    pub fn remove(context: &HuskContext, cert: &ValidCert, _demote: bool)
+        -> Result<()> {
 
-        // Check if domain list is not empty.
-        // An empty list would create an unlimited introducer.
-        if domains.is_empty() {
-            return Err(IntroducerError::UnlimitedIntroducer.into());
+        // Check if the local trust root certificate should be made an
+        // introducer, which would be an error.
+        if cert.fingerprint() == context.local_trust_root.fingerprint() {
+            return Err(IntroducerError::UnsuitableCertificate.into());
         }
 
-        // Create the SignatureBuilder with a default preconfiguration.
-        let mut builder =
-            SignatureBuilder::new(SignatureType::GenericCertification)
-            .set_signature_creation_time(std::time::SystemTime::now())?
-            .set_trust_signature(1, 120)?
-            .set_exportable_certification(false)?
-            .set_revocable(true)?;
-            // set no expiration date
-
-        // Add domains
-        for domain in domains {
-            if !mail::is_domain(domain.as_str()) {
-                return Err(IntroducerError::InvalidDomainName(domain).into());
-            }
-
-            builder = builder.add_regular_expression(format!("<[^>]+[@.]{}>$",
-                escape::regex_ctrl_escape(domain.as_str())?
-            ))?;
-        }
-
-        // For a certification, user ids are needed. Build a list of
-        // valid (non self revoked) user ids.
-        let user_ids: Vec<_> = cert.userids()
-            .filter(|u| {
-                u.self_revocations().count() == 0
-            })
-            .collect();
-
-        if user_ids.is_empty() {
-            return Err(IntroducerError::NoUserIDs(cert.fingerprint()).into());
-        }
-
-        // now certify
-        let signatures: Vec<_> = user_ids.into_iter()
-            .filter_map(|u| {
-                let b = builder.clone();
-
-                b.sign_userid_binding(
-                    &mut root_signer,
-                    cert.primary_key().key(),
-                    u.userid()).ok()
-            })
-            .collect();
-        let (new_cert, _) = cert.cert().clone().insert_packets(signatures)?;
-
-        // and (re)import
-        let new_cert = Arc::new(new_cert.into());
-        let stats = MergePublicCollectStats::new();
-        let cert_store = &context.cert_store;
-        cert_store.update_by(new_cert, &stats)?;
-
-        log::debug!("{:?}", stats);
-
-        // XXX: do something with the created stats
-        Ok(())
+        crypto::authenticate(context, cert, false, None)
     }
 }