Fix mistakenly encoding cookies to proxy

We use the cookie parser to remove the code-server token but by default
it encodes using encodeURIComponent, which encodes more than is strictly
necessary and can break proxied applications.

Now we pass the cookies through unchanged (other than removing the
code-server token).

Fixes #7927.

src/node/proxy.ts

@@ -20,17 +20,31 @@ proxy.on("error", (error, _, res) => {
   }
 })
 
+function identity<T>(val: T): T {
+  return val
+}
+
 // Strip the code-server cookie if it exists to avoid transmitting the cookie
 // to potentially malicious local ports.
 proxy.on("proxyReq", (preq, req) => {
-  const cookieSessionName = getCookieSessionName((req as Request).args["cookie-suffix"])
-  preq.setHeader(
-    "Cookie",
-    cookie.stringifyCookie({
-      ...(req as Request).cookies,
-      [cookieSessionName]: undefined,
-    }),
-  )
+  if (req.headers.cookie) {
+    const cookieSessionName = getCookieSessionName((req as Request).args["cookie-suffix"])
+    // Encoding and decoding are no-ops; we just want to remove the token
+    // without changing anything else about the cookies because not all
+    // applications encode/decode the same way `cookie` here does.
+    preq.setHeader(
+      "Cookie",
+      cookie.stringifyCookie(
+        {
+          ...cookie.parseCookie(req.headers.cookie, { decode: identity }),
+          [cookieSessionName]: undefined,
+        },
+        {
+          encode: identity,
+        },
+      ),
+    )
+  }
 })
 
 // Intercept the response to rewrite absolute redirects against the base path.