Support multiple domains on a single server.

src/api/client/session/password.rs

@@ -38,7 +38,7 @@ pub(super) async fn handle_login(
 
 	let lowercased_user_id = UserId::parse_with_server_name(
 		user_id.localpart().to_lowercase(),
-		&services.config.server_name,
+		user_id.server_name(),
 	)?;
 
 	let user_is_remote = !services.globals.user_is_local(&user_id)

src/core/config/mod.rs

@@ -88,6 +88,31 @@ pub struct Config {
 	#[cfg_attr(test, serde(default = "default_server_name"))]
 	pub server_name: OwnedServerName,
 
+	/// Alternate server names this homeserver is authoritative for. Users
+	/// with a Matrix ID on any of these domains can authenticate and use this
+	/// server, in addition to users on the primary `server_name`.
+	///
+	/// Each name must be a valid Matrix server name.
+	///
+	/// Alternate server names can be added after initialization, but should not
+	/// be removed while there exist accounts or appservice registrations using
+	/// that domain.
+	///
+	/// Each alternate domain must independently satisfy the Matrix
+	/// well-known/delegation requirements so that federation peers and clients
+	/// can resolve it to this server.
+	/// 
+	/// Note that servers providing the legacy registration endpoint can block
+	/// registration of users on alternate server names by including the full
+	/// User ID (e.g. "@user:example.com") or just the domain (e.g. ":example.com") in
+	/// `forbidden_usernames`.
+	///
+	/// example: ["legacy.example.com", "alias.example.org"]
+	/// 
+	/// default: []
+	#[serde(default)]
+	pub alternate_server_names: Vec<OwnedServerName>,
+
 	/// This is the only directory where tuwunel will save its data, including
 	/// media. Note: this was previously "/var/lib/matrix-conduit".
 	///

src/main/tests/alternate_domains.rs

@@ -0,0 +1,81 @@
+#![cfg(test)]
+
+use std::sync::Arc;
+
+use tuwunel::{Args, Runtime, Server};
+use tuwunel_core::{
+	Err, Result, ruma::
+		UserId
+	,
+};
+use tuwunel_service::Services;
+use tuwunel_service::users::Register;
+
+
+const PRIMARY: &str = "primary.example.test";
+const ALT: &str = "alt.example.test";
+
+fn alt_domain_user_id() -> &'static UserId {
+	"@bob:alt.example.test"
+		.try_into()
+		.expect("valid user id")
+}
+
+#[test]
+fn alternate_server_names_register_login_message_federate() -> Result {
+	let mut args = Args::default_test(&["fresh", "cleanup"]);
+
+	args.option
+		.push(format!("server_name=\"{PRIMARY}\""));
+	args.option
+		.push(format!("alternate_server_names=[\"{ALT}\"]"));
+
+	args.maintenance = true;
+
+	let runtime = Runtime::new(Some(&args))?;
+	let server = Server::new(Some(&args), Some(&runtime))?;
+
+	let result: Result = runtime.block_on(async {
+		let services = tuwunel::async_start(&server).await?;
+
+		let outcome = run_tests(&services).await;
+
+		server.server.shutdown()?;
+		drop(services);
+		tuwunel::async_run(&server).await?;
+		tuwunel::async_stop(&server).await?;
+
+		outcome
+	});
+
+	drop(runtime);
+	result
+}
+
+async fn run_tests(services: &Arc<Services>) -> Result {
+	test_register(services).await?;
+	Ok(())
+}
+
+/// Test that an alternate-domain user can be registered.
+async fn test_register(services: &Arc<Services>) -> Result {
+	let alternate_user_id = alt_domain_user_id();
+
+	services
+		.users
+		.full_register(Register {
+			user_id: Some(&alternate_user_id),
+			password: Some("alternateuserpassword"),
+			is_appservice: false,
+			is_guest: false,
+			grant_first_user_admin: false,
+			..Default::default()
+		})
+		.await?;
+
+	if !services.users.exists(alternate_user_id).await {
+		return Err!("({alternate_user_id}) was not found after registration");
+	}
+
+	Ok(())
+}

src/service/globals/mod.rs

@@ -100,6 +100,12 @@ impl Service {
 	#[must_use]
 	pub fn server_is_ours(&self, server_name: &ServerName) -> bool {
 		server_name == self.server_name()
+			|| self
+				.server
+				.config
+				.alternate_server_names
+				.iter()
+				.any(|s| s == server_name)
 	}
 
 	#[inline]

src/service/rooms/timeline/build.rs

@@ -160,9 +160,9 @@ pub async fn build_and_append_pdu(
 		servers.insert(state_key_uid.server_name().to_owned());
 	}
 
-	// Remove our server from the server list since it will be added to it by
-	// room_servers() and/or the if statement above
-	servers.remove(self.services.globals.server_name());
+	// Remove all servers we are authoritative for from the federation list,
+	// since they will be added to it by room_servers() and/or the if statement above.
+	servers.retain(|s| !self.services.globals.server_is_ours(s));
 
 	self.services
 		.sending

tuwunel-example.toml

@@ -37,6 +37,29 @@
 #
 #server_name =
 
+# Alternate server names this homeserver is authoritative for. Users
+# with a Matrix ID on any of these domains can authenticate and use this
+# server, in addition to users on the primary `server_name`.
+#
+# Each name must be a valid Matrix server name.
+#
+# Alternate server names can be added after initialization, but should not
+# be removed while there exist accounts or appservice registrations using
+# that domain.
+#
+# Each alternate domain must independently satisfy the Matrix
+# well-known/delegation requirements so that federation peers and clients
+# can resolve it to this server.
+# 
+# Note that servers providing the legacy registration endpoint can block
+# registration of users on alternate server names by including the full
+# User ID (e.g. "@user:example.com") or just the domain (e.g. ":example.com") in
+# `forbidden_usernames`.
+#
+# example: ["legacy.example.com", "alias.example.org"]
+#
+#alternate_server_names = []
+
 # This is the only directory where tuwunel will save its data, including
 # media. Note: this was previously "/var/lib/matrix-conduit".
 #