feat(app): better external browser Modrinth login flow (#4033)

* fix(app-frontend): do not emit exceptions when no loaders are available

* refactor(app): simplify Microsoft login code without functional changes

* feat(app): external browser auth flow for Modrinth account login

* chore: address Clippy lint

* chore(app/oauth_utils): simplify `handle_reply` error handling according to review

* chore(app-lib): simplify `Url` usage out of MC auth module

apps/app/src/api/auth.rs

@@ -33,7 +33,7 @@ pub async fn login<R: Runtime>(
     let window = tauri::WebviewWindowBuilder::new(
         &app,
         "signin",
-        tauri::WebviewUrl::External(flow.redirect_uri.parse().map_err(
+        tauri::WebviewUrl::External(flow.auth_request_uri.parse().map_err(
             |_| {
                 theseus::ErrorKind::OtherError(
                     "Error parsing auth redirect URL".to_string(),
@@ -77,6 +77,7 @@ pub async fn login<R: Runtime>(
     window.close()?;
     Ok(None)
 }
+
 #[tauri::command]
 pub async fn remove_user(user: uuid::Uuid) -> Result<()> {
     Ok(minecraft_auth::remove_user(user).await?)

apps/app/src/api/mod.rs

@@ -22,6 +22,8 @@ pub mod cache;
 pub mod friends;
 pub mod worlds;
 
+mod oauth_utils;
+
 pub type Result<T> = std::result::Result<T, TheseusSerializableError>;
 
 // // Main returnable Theseus GUI error

apps/app/src/api/mr_auth.rs

@@ -1,79 +1,70 @@
 use crate::api::Result;
-use chrono::{Duration, Utc};
+use crate::api::TheseusSerializableError;
+use crate::api::oauth_utils;
+use tauri::Manager;
+use tauri::Runtime;
 use tauri::plugin::TauriPlugin;
-use tauri::{Manager, Runtime, UserAttentionType};
+use tauri_plugin_opener::OpenerExt;
 use theseus::prelude::*;
+use tokio::sync::oneshot;
 
 pub fn init<R: tauri::Runtime>() -> TauriPlugin<R> {
     tauri::plugin::Builder::new("mr-auth")
-        .invoke_handler(tauri::generate_handler![modrinth_login, logout, get,])
+        .invoke_handler(tauri::generate_handler![
+            modrinth_login,
+            logout,
+            get,
+            cancel_modrinth_login,
+        ])
         .build()
 }
 
 #[tauri::command]
 pub async fn modrinth_login<R: Runtime>(
     app: tauri::AppHandle<R>,
-) -> Result<Option<ModrinthCredentials>> {
-    let redirect_uri = mr_auth::authenticate_begin_flow();
+) -> Result<ModrinthCredentials> {
+    let (auth_code_recv_socket_tx, auth_code_recv_socket) = oneshot::channel();
+    let auth_code = tokio::spawn(oauth_utils::auth_code_reply::listen(
+        auth_code_recv_socket_tx,
+    ));
 
-    let start = Utc::now();
+    let auth_code_recv_socket = auth_code_recv_socket.await.unwrap()?;
 
-    if let Some(window) = app.get_webview_window("modrinth-signin") {
-        window.close()?;
-    }
+    let auth_request_uri = format!(
+        "{}?launcher=true&ipver={}&port={}",
+        mr_auth::authenticate_begin_flow(),
+        if auth_code_recv_socket.is_ipv4() {
+            "4"
+        } else {
+            "6"
+        },
+        auth_code_recv_socket.port()
+    );
 
-    let window = tauri::WebviewWindowBuilder::new(
-        &app,
-        "modrinth-signin",
-        tauri::WebviewUrl::External(redirect_uri.parse().map_err(|_| {
-            theseus::ErrorKind::OtherError(
-                "Error parsing auth redirect URL".to_string(),
+    app.opener()
+        .open_url(auth_request_uri, None::<&str>)
+        .map_err(|e| {
+            TheseusSerializableError::Theseus(
+                theseus::ErrorKind::OtherError(format!(
+                    "Failed to open auth request URI: {e}"
+                ))
+                .into(),
             )
-            .as_error()
-        })?),
-    )
-    .min_inner_size(420.0, 632.0)
-    .inner_size(420.0, 632.0)
-    .max_inner_size(420.0, 632.0)
-    .zoom_hotkeys_enabled(false)
-    .title("Sign into Modrinth")
-    .always_on_top(true)
-    .center()
-    .build()?;
+        })?;
 
-    window.request_user_attention(Some(UserAttentionType::Critical))?;
+    let Some(auth_code) = auth_code.await.unwrap()? else {
+        return Err(TheseusSerializableError::Theseus(
+            theseus::ErrorKind::OtherError("Login canceled".into()).into(),
+        ));
+    };
 
-    while (Utc::now() - start) < Duration::minutes(10) {
-        if window.title().is_err() {
-            // user closed window, cancelling flow
-            return Ok(None);
-        }
+    let credentials = mr_auth::authenticate_finish_flow(&auth_code).await?;
 
-        if window
-            .url()?
-            .as_str()
-            .starts_with("https://launcher-files.modrinth.com")
-        {
-            let url = window.url()?;
-
-            let code = url.query_pairs().find(|(key, _)| key == "code");
-
-            window.close()?;
-
-            return if let Some((_, code)) = code {
-                let val = mr_auth::authenticate_finish_flow(&code).await?;
-
-                Ok(Some(val))
-            } else {
-                Ok(None)
-            };
-        }
-
-        tokio::time::sleep(std::time::Duration::from_millis(50)).await;
+    if let Some(main_window) = app.get_window("main") {
+        main_window.set_focus().ok();
     }
 
-    window.close()?;
-    Ok(None)
+    Ok(credentials)
 }
 
 #[tauri::command]
@@ -85,3 +76,8 @@ pub async fn logout() -> Result<()> {
 pub async fn get() -> Result<Option<ModrinthCredentials>> {
     Ok(theseus::mr_auth::get_credentials().await?)
 }
+
+#[tauri::command]
+pub fn cancel_modrinth_login() {
+    oauth_utils::auth_code_reply::stop_listeners();
+}

apps/app/src/api/oauth_utils/auth_code_reply.rs

@@ -0,0 +1,159 @@
+//! A minimal OAuth 2.0 authorization code grant flow redirection/reply loopback URI HTTP
+//! server implementation, compliant with [RFC 6749]'s authorization code grant flow and
+//! [RFC 8252]'s best current practices for OAuth 2.0 in native apps.
+//!
+//! This server is needed for the step 4 of the OAuth authentication dance represented in
+//! figure 1 of [RFC 8252].
+//!
+//! Further reading: https://www.oauth.com/oauth2-servers/oauth-native-apps/redirect-urls-for-native-apps/
+//!
+//! [RFC 6749]: https://datatracker.ietf.org/doc/html/rfc6749
+//! [RFC 8252]: https://datatracker.ietf.org/doc/html/rfc8252
+
+use std::{
+    net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr},
+    sync::{LazyLock, Mutex},
+    time::Duration,
+};
+
+use hyper::body::Incoming;
+use hyper_util::rt::{TokioIo, TokioTimer};
+use theseus::ErrorKind;
+use tokio::{
+    net::TcpListener,
+    sync::{broadcast, oneshot},
+};
+
+static SERVER_SHUTDOWN: LazyLock<broadcast::Sender<()>> =
+    LazyLock::new(|| broadcast::channel(1024).0);
+
+/// Starts a temporary HTTP server to receive OAuth 2.0 authorization code grant flow redirects
+/// on a loopback interface with an ephemeral port. The caller can know the bound socket address
+/// by listening on the counterpart channel for `listen_socket_tx`.
+///
+/// If the server is stopped before receiving an authorization code, `Ok(None)` is returned.
+pub async fn listen(
+    listen_socket_tx: oneshot::Sender<Result<SocketAddr, theseus::Error>>,
+) -> Result<Option<String>, theseus::Error> {
+    // IPv4 is tried first for the best compatibility and performance with most systems.
+    // IPv6 is also tried in case IPv4 is not available. Resolving "localhost" is avoided
+    // to prevent failures deriving from improper name resolution setup. Any available
+    // ephemeral port is used to prevent conflicts with other services. This is all as per
+    // RFC 8252's recommendations
+    const ANY_LOOPBACK_SOCKET: &[SocketAddr] = &[
+        SocketAddr::new(IpAddr::V4(Ipv4Addr::LOCALHOST), 0),
+        SocketAddr::new(IpAddr::V6(Ipv6Addr::LOCALHOST), 0),
+    ];
+
+    let listener = match TcpListener::bind(ANY_LOOPBACK_SOCKET).await {
+        Ok(listener) => {
+            listen_socket_tx
+                .send(listener.local_addr().map_err(|e| {
+                    ErrorKind::OtherError(format!(
+                        "Failed to get auth code reply socket address: {e}"
+                    ))
+                    .into()
+                }))
+                .ok();
+
+            listener
+        }
+        Err(e) => {
+            let error_msg =
+                format!("Failed to bind auth code reply socket: {e}");
+
+            listen_socket_tx
+                .send(Err(ErrorKind::OtherError(error_msg.clone()).into()))
+                .ok();
+
+            return Err(ErrorKind::OtherError(error_msg).into());
+        }
+    };
+
+    let mut auth_code = Mutex::new(None);
+    let mut shutdown_notification = SERVER_SHUTDOWN.subscribe();
+
+    while auth_code.get_mut().unwrap().is_none() {
+        let client_socket = tokio::select! {
+            biased;
+            _ = shutdown_notification.recv() => {
+                break;
+            }
+            conn_accept_result = listener.accept() => {
+                match conn_accept_result {
+                    Ok((socket, _)) => socket,
+                    Err(e) => {
+                        tracing::warn!("Failed to accept auth code reply: {e}");
+                        continue;
+                    }
+                }
+            }
+        };
+
+        if let Err(e) = hyper::server::conn::http1::Builder::new()
+            .keep_alive(false)
+            .header_read_timeout(Duration::from_secs(5))
+            .timer(TokioTimer::new())
+            .auto_date_header(false)
+            .serve_connection(
+                TokioIo::new(client_socket),
+                hyper::service::service_fn(|req| handle_reply(req, &auth_code)),
+            )
+            .await
+        {
+            tracing::warn!("Failed to handle auth code reply: {e}");
+        }
+    }
+
+    Ok(auth_code.into_inner().unwrap())
+}
+
+/// Stops any active OAuth 2.0 authorization code grant flow reply listening HTTP servers.
+pub fn stop_listeners() {
+    SERVER_SHUTDOWN.send(()).ok();
+}
+
+async fn handle_reply(
+    req: hyper::Request<Incoming>,
+    auth_code_out: &Mutex<Option<String>>,
+) -> Result<hyper::Response<String>, hyper::http::Error> {
+    if req.method() != hyper::Method::GET {
+        return hyper::Response::builder()
+            .status(hyper::StatusCode::METHOD_NOT_ALLOWED)
+            .header("Allow", "GET")
+            .body("".into());
+    }
+
+    // The authorization code is guaranteed to be sent as a "code" query parameter
+    // in the request URI query string as per RFC 6749 § 4.1.2
+    let auth_code = req.uri().query().and_then(|query_string| {
+        query_string
+            .split('&')
+            .filter_map(|query_pair| query_pair.split_once('='))
+            .find_map(|(key, value)| (key == "code").then_some(value))
+    });
+
+    let response = if let Some(auth_code) = auth_code {
+        *auth_code_out.lock().unwrap() = Some(auth_code.to_string());
+
+        hyper::Response::builder()
+            .status(hyper::StatusCode::OK)
+            .header("Content-Type", "text/html;charset=utf-8")
+            .body(
+                include_str!("auth_code_reply/page.html")
+                    .replace("{{title}}", "Success")
+                    .replace("{{message}}", "You have successfully signed in! You can close this page now."),
+            )
+    } else {
+        hyper::Response::builder()
+            .status(hyper::StatusCode::BAD_REQUEST)
+            .header("Content-Type", "text/html;charset=utf-8")
+            .body(
+                include_str!("auth_code_reply/page.html")
+                    .replace("{{title}}", "Error")
+                    .replace("{{message}}", "Authorization code not found. Please try signing in again."),
+            )
+    }?;
+
+    Ok(response)
+}

apps/app/src/api/oauth_utils/mod.rs

@@ -0,0 +1,3 @@
+//! Assorted utilities for OAuth 2.0 authorization flows.
+
+pub mod auth_code_reply;