diff --git a/next.config.mjs b/next.config.mjs
index 65729ee..5c5c2e4 100644
--- a/next.config.mjs
+++ b/next.config.mjs
@@ -83,6 +83,27 @@ const securityHeaders = [
     key: "Permissions-Policy",
     value: "camera=(), microphone=(), geolocation=(), payment=()",
   },
+  {
+    key: "Cross-Origin-Opener-Policy",
+    value: "same-origin",
+  },
+  {
+    key: "Cross-Origin-Embedder-Policy",
+    value: "credentialless",
+  },
+  {
+    key: "Cross-Origin-Resource-Policy",
+    value: "same-origin",
+  },
+  // HSTS only in production so local HTTP development keeps working.
+  ...(isDev
+    ? []
+    : [
+        {
+          key: "Strict-Transport-Security",
+          value: "max-age=63072000; includeSubDomains; preload",
+        },
+      ]),
 ];
 
 const nextConfig = {
diff --git a/src/components/shared/wallet-error-banner.tsx b/src/components/shared/wallet-error-banner.tsx
index a5a78bf..86cec42 100644
--- a/src/components/shared/wallet-error-banner.tsx
+++ b/src/components/shared/wallet-error-banner.tsx
@@ -1,7 +1,9 @@
 "use client";
 
+import { useEffect, useState } from "react";
 import { AlertTriangle, X, ExternalLink } from "lucide-react";
 import type { WalletError } from "@/lib/hooks/use-auth";
+import { getSelectedWalletId, type WalletProviderId } from "@/lib/stellar/wallet";
 
 interface WalletErrorBannerProps {
   error: WalletError;
@@ -9,11 +11,41 @@ interface WalletErrorBannerProps {
   onRetry?: () => void;
 }
 
+const WALLET_INSTALL_LINKS: Record<
+  WalletProviderId,
+  { name: string; url: string }
+> = {
+  freighter: { name: "Freighter", url: "https://www.freighter.app/" },
+  lobstr: { name: "LOBSTR", url: "https://lobstr.co/" },
+  rabet: { name: "Rabet", url: "https://rabet.io/" },
+};
+
+const ALL_WALLETS = Object.values(WALLET_INSTALL_LINKS);
+
+function resolveInstallLinks(
+  walletId: string | null
+): Array<{ name: string; url: string }> {
+  if (walletId && walletId in WALLET_INSTALL_LINKS) {
+    return [
+      WALLET_INSTALL_LINKS[walletId as WalletProviderId],
+    ];
+  }
+  return ALL_WALLETS;
+}
+
 export function WalletErrorBanner({
   error,
   onDismiss,
   onRetry,
 }: WalletErrorBannerProps) {
+  const [walletId, setWalletId] = useState<string | null>(null);
+
+  useEffect(() => {
+    setWalletId(getSelectedWalletId());
+  }, []);
+
+  const installLinks = resolveInstallLinks(walletId);
+
   return (
     <div
       role="alert"
@@ -25,15 +57,20 @@ export function WalletErrorBanner({
           <p className="text-sm font-medium text-red-800">{error.message}</p>
           <p className="text-sm text-red-600 mt-1">{error.resolution}</p>
           {error.type === "not_installed" && (
-            <a
-              href="https://www.freighter.app/"
-              target="_blank"
-              rel="noopener noreferrer"
-              className="inline-flex items-center gap-1 text-sm text-red-700 underline mt-2 hover:text-red-900"
-            >
-              Get Freighter
-              <ExternalLink className="h-3 w-3" />
-            </a>
+            <div className="mt-2 flex flex-wrap gap-x-3 gap-y-1">
+              {installLinks.map((wallet) => (
+                <a
+                  key={wallet.name}
+                  href={wallet.url}
+                  target="_blank"
+                  rel="noopener noreferrer"
+                  className="inline-flex items-center gap-1 text-sm text-red-700 underline hover:text-red-900"
+                >
+                  Get {wallet.name}
+                  <ExternalLink className="h-3 w-3" />
+                </a>
+              ))}
+            </div>
           )}
           {onRetry && (
             <button
diff --git a/src/lib/api/client.test.ts b/src/lib/api/client.test.ts
index 53a8fb1..5631be1 100644
--- a/src/lib/api/client.test.ts
+++ b/src/lib/api/client.test.ts
@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
-import { apiClient, isAbortError } from "./client";
+import { apiClient, hashJwtForCacheKey, isAbortError } from "./client";
 import { useErrorStore } from "@/store/error-store";
 
 // zustand's persist middleware writes on every set(); jsdom's localStorage is
@@ -447,3 +447,38 @@ describe("apiClient cache behaviour (issue #312)", () => {
   });
 });
 
+// ── Issue #542: JWT must not appear in cache keys ────────────────────────────
+
+describe("apiClient cache keys (issue #542)", () => {
+  const sampleJwt =
+    "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ1c2VyLTEif0.signature";
+
+  it("does not embed the raw JWT in the hashed cache key component", () => {
+    const hashed = hashJwtForCacheKey(sampleJwt);
+
+    expect(hashed).not.toContain(sampleJwt);
+    expect(hashed).not.toContain("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9");
+    expect(hashed).not.toContain("signature");
+  });
+
+  it("hashes deterministically so cache hit/miss behaviour is unchanged", () => {
+    expect(hashJwtForCacheKey(sampleJwt)).toBe(hashJwtForCacheKey(sampleJwt));
+  });
+
+  it("distinguishes different tokens", () => {
+    expect(hashJwtForCacheKey("token-a")).not.toBe(hashJwtForCacheKey("token-b"));
+  });
+
+  it("serves a cache hit for the same token and a miss for a different one", async () => {
+    fetchMock.mockResolvedValueOnce(jsonResponse({ data: "user-1" }));
+    await apiClient.get("/cache-jwt", "jwt-user-1");
+    await apiClient.get("/cache-jwt", "jwt-user-1");
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+
+    fetchMock.mockResolvedValueOnce(jsonResponse({ data: "user-2" }));
+    const other = await apiClient.get("/cache-jwt", "jwt-user-2");
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expect(other).toEqual({ data: "user-2" });
+  });
+});
+
diff --git a/src/lib/api/client.ts b/src/lib/api/client.ts
index a854de3..3dd1755 100644
--- a/src/lib/api/client.ts
+++ b/src/lib/api/client.ts
@@ -77,6 +77,23 @@ type CacheEntry = {
   expiresAt: number;
 };
 
+/**
+ * Fast non-cryptographic digest of a JWT for cache keying (#542).
+ * Two independent FNV-1a streams yield a 64-bit hex digest so the raw
+ * token never appears in heap-dumpable cache key strings, while cache
+ * hit/miss behaviour stays deterministic per token.
+ */
+export function hashJwtForCacheKey(jwt: string): string {
+  let h1 = 0x811c9dc5;
+  let h2 = 0x01000193;
+  for (let i = 0; i < jwt.length; i++) {
+    const c = jwt.charCodeAt(i);
+    h1 = Math.imul(h1 ^ c, 0x01000193);
+    h2 = Math.imul(h2 ^ c, 0x85ebca6b);
+  }
+  return `${(h1 >>> 0).toString(16)}${(h2 >>> 0).toString(16)}`;
+}
+
 const responseCache = new Map<string, CacheEntry>();
 
 /**
@@ -377,7 +394,7 @@ class ApiClient {
   }
 
   private cacheKey(url: string, jwt?: string): string {
-    return jwt ? `${url}|${jwt}` : url;
+    return jwt ? `${url}|${hashJwtForCacheKey(jwt)}` : url;
   }
 
   /**
diff --git a/src/middleware.test.ts b/src/middleware.test.ts
index fc605d7..48bfe63 100644
--- a/src/middleware.test.ts
+++ b/src/middleware.test.ts
@@ -168,6 +168,59 @@ describe("auth routes", () => {
   });
 });
 
+describe("open redirect protection (#541)", () => {
+  it("rejects an absolute https URL in the redirect parameter", () => {
+    const target = redirectTarget(
+      middleware(makeRequest("/connect", "jwt-abc", "?redirect=https://evil.com"))
+    );
+
+    expect(target?.pathname).toBe("/dashboard");
+    expect(target?.hostname).not.toBe("evil.com");
+  });
+
+  it("rejects an absolute http URL with a path", () => {
+    const target = redirectTarget(
+      middleware(
+        makeRequest("/connect", "jwt-abc", "?redirect=http://evil.com/phish")
+      )
+    );
+
+    expect(target?.pathname).toBe("/dashboard");
+  });
+
+  it("rejects a protocol-relative URL", () => {
+    const target = redirectTarget(
+      middleware(makeRequest("/connect", "jwt-abc", "?redirect=//evil.com"))
+    );
+
+    expect(target?.pathname).toBe("/dashboard");
+  });
+
+  it("rejects a backslash-based open redirect", () => {
+    const target = redirectTarget(
+      middleware(makeRequest("/connect", "jwt-abc", "?redirect=/%5Cevil.com"))
+    );
+
+    expect(target?.pathname).toBe("/dashboard");
+  });
+
+  it("still honours a safe relative path", () => {
+    const target = redirectTarget(
+      middleware(makeRequest("/connect", "jwt-abc", "?redirect=/courses/course-1/quiz"))
+    );
+
+    expect(target?.pathname).toBe("/courses/course-1/quiz");
+  });
+
+  it("falls back to /dashboard when redirect is empty", () => {
+    const target = redirectTarget(
+      middleware(makeRequest("/connect", "jwt-abc", "?redirect="))
+    );
+
+    expect(target?.pathname).toBe("/dashboard");
+  });
+});
+
 describe("matcher", () => {
   it("covers every protected area and both auth routes", () => {
     expect(config.matcher).toEqual(
diff --git a/src/middleware.ts b/src/middleware.ts
index 8ffdaa4..3206b1e 100644
--- a/src/middleware.ts
+++ b/src/middleware.ts
@@ -47,6 +47,26 @@ function isAuthRoute(pathname: string): boolean {
   return AUTH_PREFIXES.some((prefix) => pathname.startsWith(prefix));
 }
 
+/**
+ * Reject open-redirect targets (#541). Only same-origin relative paths are
+ * allowed: must start with a single "/", must not be protocol-relative
+ * ("//evil.com"), and must not embed a scheme ("https://evil.com").
+ */
+function isSafeRedirectPath(redirect: string | null): redirect is string {
+  if (!redirect) return false;
+  if (!redirect.startsWith("/")) return false;
+  if (redirect.startsWith("//")) return false;
+  if (redirect.includes("://")) return false;
+  if (redirect.includes("\\")) return false;
+  return true;
+}
+
+/**
+ * Decode JWT payload and check expiry (#495).
+ * Uses atob() for base64 decoding — works in Edge runtime.
+ * Malformed tokens are treated as expired.
+ */
+function isJwtExpired(token: string): boolean {
 /** Validate JWT structure and expiry; signature verification remains server-side. */
 function isValidSessionToken(token: string): boolean {
   try {
@@ -124,7 +144,7 @@ export function middleware(request: NextRequest) {
     if (validSession) {
       const redirect = request.nextUrl.searchParams.get("redirect");
       const url = request.nextUrl.clone();
-      url.pathname = redirect || "/dashboard";
+      url.pathname = isSafeRedirectPath(redirect) ? redirect : "/dashboard";
       url.searchParams.delete("redirect");
       return NextResponse.redirect(url);
     }