fix(webapp): restore magic link login on the login page (#4220)

## Summary

Magic link login could appear completely broken: submitting your email
on the login page showed a stale "This email is unauthorized" error
instead of the "we've sent you a magic link" confirmation, even when the
address was fine.

This PR reverts
[#4215](#4215) (whose
diagnosis and fix turned out to be wrong) and fixes the actual bug,
which was in how login errors are stored and consumed.

## Root cause

Two session bugs compounded on the login page:

- The `/login` loader read the flashed `auth:error` without committing
the session. A Remix flash is only consumed when the session is
committed after the read, so once any attempt flashed an error (for
example an address rejected on an instance with `WHITELISTED_EMAILS`
set), it stayed in the session cookie and reappeared on every later
`/login` visit, making successful attempts look like failures.
- The `/login/magic` action stored its validation and rate limit errors
with `session.set`, which survives every later read and commit, so those
errors stuck permanently.

[#4215](#4215) had
instead diagnosed a server-only module leaking into the client bundle
and crashing navigation. Checking the shipped images' client bundles via
their sourcemaps shows `.server` modules were always stubbed out, so
that change fixed nothing and is reverted here.

## Fix

- `/login` reads the flashed error and commits the session when one was
present, so an error renders once and clears. The `redirectTo` branch
now surfaces the error too instead of leaving it in the cookie.
- `/login/magic` flashes its errors instead of `set`ting them.

Verified end-to-end on a live preview environment: a rejected address
shows the error once and a reload clears it; a valid address lands on
the confirmation screen with the address named; GitHub, Google, and SSO
login paths are untouched by this diff.

Author: samejr

.server-changes/clearer-whitelist-login-error.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Clearer login error when an email address is blocked by the WHITELISTED_EMAILS setting: the message now explains the address isn't allowed on this instance instead of the ambiguous "This email is unauthorized".

.server-changes/consume-stale-login-errors.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: fix
+---
+
+Fixed stale login errors: an error from a previous login attempt (for example a rejected email address) no longer keeps reappearing on the login page and no longer makes later, successful attempts look like they failed.

apps/webapp/app/routes/login._index/route.tsx

@@ -23,7 +23,10 @@ import { isGithubAuthSupported, isGoogleAuthSupported } from "~/services/auth.se
 import { getLastAuthMethod } from "~/services/lastAuthMethod.server";
 import { commitSession, setRedirectTo } from "~/services/redirectTo.server";
 import { getUserId } from "~/services/session.server";
-import { getUserSession } from "~/services/sessionStorage.server";
+import {
+  commitSession as commitUserSession,
+  getUserSession,
+} from "~/services/sessionStorage.server";
 import { ssoController } from "~/services/sso.server";
 import { flags as getGlobalFlags } from "~/v3/featureFlags.server";
 import { requestUrl } from "~/utils/requestUrl.server";
@@ -111,8 +114,36 @@ export async function loader({ request }: LoaderFunctionArgs) {
     showSsoAuth = (globalFlags as Record<string, unknown>).hasSso === true;
   }
 
+  // Read the flashed auth error and, when one exists, commit the session so
+  // the flash is consumed. Reading without committing leaves the flash in the
+  // cookie, so a stale error (e.g. a once-rejected email address) would
+  // resurface on every future /login visit and make later, successful login
+  // attempts look like they failed.
+  const userSession = await getUserSession(request);
+  const error = userSession.get("auth:error");
+  // get() only auto-clears flash-stored values. Sessions written before this
+  // fix stored the error with set(), which survives get() + commit — unset it
+  // explicitly so those sessions heal too instead of showing the stale error
+  // until the cookie's one-year maxAge runs out.
+  userSession.unset("auth:error");
+
+  let authError: string | undefined;
+  if (error) {
+    if ("message" in error) {
+      authError = error.message;
+    } else {
+      authError = JSON.stringify(error, null, 2);
+    }
+  }
+
+  const headers = new Headers();
+  if (error) {
+    headers.append("Set-Cookie", await commitUserSession(userSession));
+  }
+
   if (redirectTo) {
     const session = await setRedirectTo(request, redirectTo);
+    headers.append("Set-Cookie", await commitSession(session));
 
     return typedjson(
       {
@@ -121,39 +152,26 @@ export async function loader({ request }: LoaderFunctionArgs) {
         showGoogleAuth: isGoogleAuthSupported,
         showSsoAuth,
         lastAuthMethod,
-        authError: null,
+        authError,
         notice,
         isVercelMarketplace: redirectTo.startsWith("/vercel/callback"),
       },
-      {
-        headers: {
-          "Set-Cookie": await commitSession(session),
-        },
-      }
+      { headers }
     );
   } else {
-    const session = await getUserSession(request);
-    const error = session.get("auth:error");
-
-    let authError: string | undefined;
-    if (error) {
-      if ("message" in error) {
-        authError = error.message;
-      } else {
-        authError = JSON.stringify(error, null, 2);
-      }
-    }
-
-    return typedjson({
-      redirectTo: null,
-      showGithubAuth: isGithubAuthSupported,
-      showGoogleAuth: isGoogleAuthSupported,
-      showSsoAuth,
-      lastAuthMethod,
-      authError,
-      notice,
-      isVercelMarketplace: false,
-    });
+    return typedjson(
+      {
+        redirectTo: null,
+        showGithubAuth: isGithubAuthSupported,
+        showGoogleAuth: isGoogleAuthSupported,
+        showSsoAuth,
+        lastAuthMethod,
+        authError,
+        notice,
+        isVercelMarketplace: false,
+      },
+      { headers }
+    );
   }
 }
 

apps/webapp/app/routes/login.magic/magicLinkEmailCookie.server.ts

@@ -0,0 +1,15 @@
+import { createCookie } from "@remix-run/node";
+import { env } from "~/env.server";
+
+// Carries the submitted email to the confirmation screen in a short-lived,
+// httpOnly cookie rather than the URL, so the address never lands in access
+// logs, browser history, or error-tracker breadcrumbs. Lives in a .server
+// module: it calls createCookie at import time using server-only env, which
+// throws if it ever evaluates in the client bundle.
+export const magicLinkEmailCookie = createCookie("magiclink-email", {
+  maxAge: 60 * 10,
+  httpOnly: true,
+  sameSite: "lax",
+  secure: env.NODE_ENV === "production",
+  path: "/",
+});

apps/webapp/app/routes/login.magic/route.tsx

@@ -34,6 +34,7 @@ import { ssoRedirectForEmail } from "~/services/ssoAutoDiscovery.server";
 import { logger, tryCatch } from "@trigger.dev/core/v3";
 import { env } from "~/env.server";
 import { extractClientIp } from "~/utils/extractClientIp.server";
+import { magicLinkEmailCookie } from "./magicLinkEmailCookie.server";
 
 export const meta: MetaFunction = ({ matches }) => {
   const parentMeta = matches
@@ -73,14 +74,12 @@ export async function loader({ request }: LoaderFunctionArgs) {
   // confirmation renders the flashed error as magicLinkError below.
   const url = new URL(request.url);
   const sanitized = sanitizeRedirectPath(url.searchParams.get("redirectTo"));
-  // The email-link strategy stores the submitted address in the session
-  // (`auth:email`) alongside the magic-link key, so read it from there to name
-  // the confirmation — no address in the URL, and no separate cookie to leak
-  // into the client bundle. Validate before echoing it back.
-  const emailValue = session.get("auth:email");
+  // The submitted address is carried in a short-lived cookie (not the URL) so
+  // the confirmation can name it. Validate before echoing it back.
+  const emailCookie = await magicLinkEmailCookie.parse(request.headers.get("Cookie"));
   const email =
-    typeof emailValue === "string" && z.string().email().safeParse(emailValue).success
-      ? emailValue
+    typeof emailCookie === "string" && z.string().email().safeParse(emailCookie).success
+      ? emailCookie
       : null;
   if (!session.has("triggerdotdev:magiclink")) {
     // Throw (not return) so the redirect doesn't widen the loader's return
@@ -92,6 +91,9 @@ export async function loader({ request }: LoaderFunctionArgs) {
   }
 
   const error = session.get("auth:error");
+  // Same migration hygiene as /login: pre-fix sessions stored this with
+  // set(), which get() doesn't clear — unset so the commit below removes it.
+  session.unset("auth:error");
 
   const redirectTo = sanitized === "/" ? null : sanitized;
   const headers = new Headers();
@@ -142,7 +144,9 @@ export async function action({ request }: ActionFunctionArgs) {
 
   if (!result.success) {
     const session = await getUserSession(request);
-    session.set("auth:error", {
+    // flash, not set: a set() key survives every later read/commit, so the
+    // error would reappear on each /login visit long after the failed attempt.
+    session.flash("auth:error", {
       message: "Please enter a valid email address.",
     });
 
@@ -192,7 +196,8 @@ export async function action({ request }: ActionFunctionArgs) {
               : "Failed sending magic link. Please try again shortly.";
 
           const session = await getUserSession(request);
-          session.set("auth:error", {
+          // flash, not set — same one-shot semantics as the validation error above.
+          session.flash("auth:error", {
             message: errorMessage,
           });
 
@@ -216,13 +221,20 @@ export async function action({ request }: ActionFunctionArgs) {
         return redirect(ssoRedirect);
       }
 
-      // The email-link strategy stores the address in the session (`auth:email`)
-      // and throws its own redirect Response (with the committed session cookie),
-      // so return it directly — the confirmation reads the email from the session.
-      return await authenticator.authenticate("email-link", request, {
-        successRedirect: "/login/magic",
-        failureRedirect: "/login",
-      });
+      // authenticator.authenticate throws its redirect Response; attach the
+      // sent-to email as a short-lived cookie so the confirmation can name it
+      // without putting the address in the URL.
+      try {
+        return await authenticator.authenticate("email-link", request, {
+          successRedirect: "/login/magic",
+          failureRedirect: "/login",
+        });
+      } catch (thrown) {
+        if (thrown instanceof Response) {
+          thrown.headers.append("Set-Cookie", await magicLinkEmailCookie.serialize(email));
+        }
+        throw thrown;
+      }
     }
     case "reset":
     default: {

apps/webapp/app/services/emailAuth.server.tsx

@@ -18,11 +18,6 @@ const emailStrategy = new EmailLinkStrategy(
     secret,
     callbackURL: "/magic",
     sessionMagicLinkKey: "triggerdotdev:magiclink",
-    // Pin explicitly to the library default rather than relying on it: the
-    // /login/magic loader reads the submitted address via
-    // session.get("auth:email") to name it on the confirmation screen, so a
-    // future remix-auth-email-link default change can't silently break that.
-    sessionEmailKey: "auth:email",
   },
   async ({
     email,

apps/webapp/app/utils/email.ts

@@ -7,6 +7,8 @@ export function assertEmailAllowed(email: string) {
   }
 
   if (!emailMatchesPattern(env.WHITELISTED_EMAILS, email)) {
-    throw new Error("This email is unauthorized");
+    // Surfaced verbatim on the login page. Name the actual policy so a
+    // rejection on a restricted instance reads as configuration, not a bug.
+    throw new Error("This email address isn't allowed to sign in on this instance.");
   }
 }