redirect on private struct

index.js

@@ -77,6 +77,11 @@ app.use("/plumbing", require("./plumbing"));
 // list, exactly like its user-facing routes do.
 app.param("structure_id", (req, res, next, id) => {
   if (!model.canAccessStructure(req.session.userId, id)) {
+    // Logged-out visitors get a chance to sign in and come back; logged-in
+    // non-members stay 404 so we never confirm the structure exists to them.
+    if (!req.session.userId && req.method === "GET") {
+      return res.redirect("/login?next=" + encodeURIComponent(req.originalUrl));
+    }
     return res.status(404).send("Not found");
   }
   next();
@@ -373,46 +378,61 @@ buildRoutes();
 // |       | _____| ||   |___ |   |  | |
 // |_______||_______||_______||___|  |_|
 
+// Only same-site absolute paths survive as post-login redirect targets, so a
+// crafted ?next= can't bounce someone to another origin (open redirect). A
+// leading `//` is protocol-relative and would escape our origin, so reject it.
+function safeNext(next) {
+  if (typeof next !== "string" || !next.startsWith("/") || next.startsWith("//")) {
+    return null;
+  }
+  return next;
+}
+
 app.post("/register", async (req, res) => {
+  const next = safeNext(req.body.next);
   try {
     const { username, password } = req.body;
     const hashedPassword = await bcrypt.hash(password, 10); // 10 is the saltRounds
     const userId = model.createUser(username, hashedPassword);
     req.session.userId = userId;
-    res.redirect("/workshop");
+    res.redirect(next || "/workshop");
   } catch (e) {
-    return res.send(eta.render("auth/register", { error: e }));
+    return res.send(eta.render("auth/register", { error: e, next }));
   }
 });
 
 app.post("/login", async (req, res) => {
   const { username, password } = req.body;
+  const next = safeNext(req.body.next);
   const user = model.getUser(username);
 
   if (user && (await bcrypt.compare(password, user.password))) {
     req.session.userId = user.id;
-    return res.redirect("/");
+    return res.redirect(next || "/");
   }
 
   return res.send(
     eta.render("auth/login", {
       error: "are you sure you entered that right?",
+      next,
     }),
   );
 });
 
 app.get("/register", async (req, res) => {
+  const next = safeNext(req.query.next);
   if (req.session.userId) {
-    return res.redirect("/");
+    return res.redirect(next || "/");
   }
-  return res.send(eta.render("auth/register", { error: null }));
+  return res.send(eta.render("auth/register", { error: null, next }));
 });
 
 app.get("/login", async (req, res) => {
+  const next = safeNext(req.query.next);
   if (req.session.userId) {
-    return res.redirect("/");
+    return res.redirect(next || "/");
   }
-  return res.send(eta.render("auth/login", { error: null }));
+  return res.send(eta.render("auth/login", { error: null, next }));
 });
 
 app.all("/logout", async (req, res) => {
@@ -1068,8 +1088,13 @@ app.all("*", async (req, res) => {
       const route = routeMatch.route;
 
       // Private structures are invisible to uninvited users: 404, so a private
-      // route is indistinguishable from one that doesn't exist.
+      // route is indistinguishable from one that doesn't exist. Logged-out
+      // visitors on a GET get bounced to login and returned here afterward;
+      // logged-in non-members still 404.
       if (!model.canAccessStructure(req.session.userId, route.structure_id)) {
+        if (!req.session.userId && verb === "GET") {
+          return res.redirect("/login?next=" + encodeURIComponent(req.originalUrl));
+        }
         return res.status(404).json({ success: false, message: "Path not found" });
       }
 

views/auth/login.eta

@@ -1,12 +1,13 @@
 <form action="/login" method="POST">
+    <% if (it.next) { %><input type="hidden" name="next" value="<%= it.next %>"><% } %>
     <input name="username" placeholder="username">
     <input name="password" placeholder="password">
     <button type="submit">
         come home
     </button>
     <% if (it.error) { %>
-    <%= error %>
+    <%= it.error %>
     <% } %>
     <br>
-    <div> or you can <a href="/register">move in here</a>.
+    <div> or you can <a href="/register<%= it.next ? '?next=' + encodeURIComponent(it.next) : '' %>">move in here</a>.
 </form>

views/auth/register.eta

@@ -1,4 +1,5 @@
 <form action="/register" method="POST">
+    <% if (it.next) { %><input type="hidden" name="next" value="<%= it.next %>"><% } %>
     <input name="username" placeholder="username">
     <input name="password" placeholder="password">
     <button type="submit">
@@ -7,4 +8,6 @@
     <% if (it.error) { %>
     <%= it.error %>
     <% } %>
+    <br>
+    <div> or you can <a href="/login<%= it.next ? '?next=' + encodeURIComponent(it.next) : '' %>">come home</a>.
 </form>