sasl relay over s2s: authenticate plain forwarded to services (sasl_server), 900/903 on success; fails clean with no services

src/config.rs

@@ -74,6 +74,7 @@ pub struct Config {
     pub dnsbl_zones: Vec<String>,      // DNS blocklist zones to check on connect
     pub dnsbl_action: String,          // mark | kline | gline | zline (on a hit)
     pub dnsbl_reason: String,          // ban reason for a DNSBL hit
+    pub sasl_server: String,           // linked services server that handles SASL ("" = none)
 }
 
 impl Default for Config {
@@ -100,6 +101,7 @@ impl Default for Config {
             dnsbl_zones: Vec::new(),
             dnsbl_action: "mark".to_string(),
             dnsbl_reason: "Your host is listed in a DNS blocklist".to_string(),
+            sasl_server: String::new(),
         }
     }
 }
@@ -232,6 +234,7 @@ impl Config {
                 }
                 "dnsbl_action" => c.dnsbl_action = v.to_ascii_lowercase(),
                 "dnsbl_reason" => c.dnsbl_reason = v.to_string(),
+                "sasl_server" | "sasl_target" => c.sasl_server = v.to_string(),
                 _ => {}
             }
         }

src/coremods/core_rehash.rs

@@ -66,6 +66,7 @@ impl Command for Rehash {
                 s.dnsbl_zones = fresh.dnsbl_zones;
                 s.dnsbl_action = fresh.dnsbl_action;
                 s.dnsbl_reason = fresh.dnsbl_reason;
+                s.sasl_server = fresh.sasl_server;
                 s.announce("Server configuration reloaded.");
                 s.numeric(uid, RPL_REHASHING, &format!("{path} :Rehashing"));
             }

src/coremods/core_user.rs

@@ -159,18 +159,24 @@ impl Command for Authenticate {
         }
         let arg = &params[0];
         let mech = s.users.get(&uid).and_then(|u| u.sasl_mech.clone());
+        // SASL is relayed to a linked services server (see `Server::sasl_relay`);
+        // with none configured/linked it fails cleanly, exactly like InspIRCd.
+        let have_services = s.sasl_link().is_some();
         match mech {
             // step 1 — the client picks a mechanism
             None => {
-                if arg.eq_ignore_ascii_case("PLAIN") {
+                if arg == "*" {
+                    s.numeric(uid, ERR_SASLABORTED, ":SASL authentication aborted");
+                    CmdResult::Ok
+                } else if arg.eq_ignore_ascii_case("PLAIN") {
                     if let Some(u) = s.users.get_mut(&uid) {
                         u.sasl_mech = Some("PLAIN".to_string());
                     }
+                    if have_services {
+                        s.sasl_relay(uid, "S PLAIN"); // start the exchange at services
+                    }
                     s.send(uid, "AUTHENTICATE +".to_string());
                     CmdResult::Ok
-                } else if arg == "*" {
-                    s.numeric(uid, ERR_SASLABORTED, ":SASL authentication aborted");
-                    CmdResult::Ok
                 } else {
                     s.numeric(uid, RPL_SASLMECHS, "PLAIN :are available SASL mechanisms");
                     s.numeric(uid, ERR_SASLFAIL, ":Unsupported SASL mechanism");
@@ -179,19 +185,32 @@ impl Command for Authenticate {
             }
             // step 2 — the client sends the base64 payload (or aborts with `*`)
             Some(_) => {
+                if arg == "*" {
+                    if have_services {
+                        s.sasl_relay(uid, "D A");
+                    }
                     if let Some(u) = s.users.get_mut(&uid) {
                         u.sasl_mech = None;
                     }
-                if arg == "*" {
                     s.numeric(uid, ERR_SASLABORTED, ":SASL authentication aborted");
                     return CmdResult::Ok;
                 }
                 if arg.len() > 400 {
+                    if let Some(u) = s.users.get_mut(&uid) {
+                        u.sasl_mech = None;
+                    }
                     s.numeric(uid, ERR_SASLTOOLONG, ":SASL message too long");
                     return CmdResult::Fail;
                 }
-                // base64(authzid \0 authcid \0 passwd) — would be relayed to services
+                if have_services {
-                let _creds = openssl::base64::decode_block(arg).unwrap_or_default();
+                    // relay the response; the verdict (900/903 or 904) comes back
+                    // over S2S in `Server::link_sasl`, which clears `sasl_mech`.
+                    s.sasl_relay(uid, &format!("C {arg}"));
+                    CmdResult::Ok
+                } else {
+                    if let Some(u) = s.users.get_mut(&uid) {
+                        u.sasl_mech = None;
+                    }
                     s.numeric(
                         uid,
                         ERR_SASLFAIL,
@@ -201,6 +220,7 @@ impl Command for Authenticate {
                 }
             }
         }
+    }
 }
 
 /// SETNAME — change your realname (IRCv3). Broadcast to `setname`-capable peers.

src/link.rs

@@ -171,6 +171,7 @@ impl Server {
             "SVSLOGOUT" if registered => self.link_svslogout(msg),
             "ENCAP" if registered => self.link_encap(uid, msg),
             "METADATA" if registered => self.link_metadata(msg),
+            "SASL" if registered => self.link_sasl(msg),
             "BURST" => {
                 if let Some(l) = self.links.get_mut(&uid) {
                     l.bursting = true;
@@ -520,6 +521,89 @@ impl Server {
         }
     }
 
+    // --- SASL relay (client AUTHENTICATE ⇄ services) --------------------------
+
+    /// The local link toward the configured SASL services server, if connected.
+    pub fn sasl_link(&self) -> Option<Uid> {
+        if self.sasl_server.is_empty() {
+            return None;
+        }
+        self.servers
+            .values()
+            .find(|sv| sv.name == self.sasl_server)
+            .map(|sv| sv.via)
+    }
+
+    /// Relay one SASL step for local client `uid` to the services server:
+    /// `:<our-sid> SASL <client-uuid> <rest>`. No-op if SASL services aren't linked.
+    pub fn sasl_relay(&self, uid: Uid, rest: &str) {
+        let (Some(via), Some(uuid)) = (
+            self.sasl_link(),
+            self.users.get(&uid).map(|u| u.uuid.clone()),
+        ) else {
+            return;
+        };
+        self.link_out(via, format!(":{} SASL {uuid} {rest}", self.sid));
+    }
+
+    /// A SASL message from services: `:<svcsid> SASL <client-uuid> <type> …`.
+    ///   `C <data>` → relay a server challenge to the client as `AUTHENTICATE`;
+    ///   `D S [account]` → success (log in + 900/903); `D <other>` → fail (904).
+    fn link_sasl(&mut self, msg: &Message) {
+        if msg.params.len() < 2 {
+            return;
+        }
+        let Some(&uid) = self.uuid_local.get(&msg.params[0]) else {
+            return; // not one of our clients
+        };
+        match msg.params[1].as_str() {
+            "C" => {
+                if let Some(data) = msg.params.get(2) {
+                    self.send(uid, format!("AUTHENTICATE {data}"));
+                }
+            }
+            "D" => {
+                let ok = msg.params.get(2).map(|t| t == "S").unwrap_or(false);
+                let account = msg.params.get(3).cloned().unwrap_or_default();
+                if ok && !account.is_empty() {
+                    self.set_login(uid, &account);
+                }
+                self.sasl_done(uid, ok, &account);
+                if let Some(u) = self.users.get_mut(&uid) {
+                    u.sasl_mech = None;
+                }
+            }
+            _ => {}
+        }
+    }
+
+    /// Emit the SASL outcome to the client: 900 + 903 on success, 904 on failure.
+    fn sasl_done(&self, uid: Uid, success: bool, account: &str) {
+        if success {
+            let mask = self
+                .users
+                .get(&uid)
+                .map(|u| u.prefix())
+                .unwrap_or_else(|| "*".to_string());
+            self.numeric(
+                uid,
+                crate::numeric::RPL_LOGGEDIN,
+                &format!("{mask} {account} :You are now logged in as {account}"),
+            );
+            self.numeric(
+                uid,
+                crate::numeric::RPL_SASLSUCCESS,
+                ":SASL authentication successful",
+            );
+        } else {
+            self.numeric(
+                uid,
+                crate::numeric::ERR_SASLFAIL,
+                ":SASL authentication failed",
+            );
+        }
+    }
+
     // --- inbound S2S records --------------------------------------------------
 
     fn link_uid_recv(&mut self, via: Uid, msg: &Message) {

src/server.rs

@@ -103,6 +103,7 @@ pub struct Server {
     pub dnsbl_zones: Vec<String>,                  // DNS blocklist zones checked on connect
     pub dnsbl_action: String,                      // mark | kline | gline | zline
     pub dnsbl_reason: String,                      // ban reason on a DNSBL hit
+    pub sasl_server: String,                       // services server that handles SASL
     pub event_tx: Sender<Event>,                   // self-inject events (DNS results)
 }
 
@@ -142,6 +143,7 @@ impl Server {
             dnsbl_zones: cfg.dnsbl_zones,
             dnsbl_action: cfg.dnsbl_action,
             dnsbl_reason: cfg.dnsbl_reason,
+            sasl_server: cfg.sasl_server,
             event_tx,
         }
     }