Update proxy path passthrough documentation

Includes updated create-react-app docs.

Closes #2565

Author: nhooyr

docs/FAQ.md

@@ -16,6 +16,7 @@
   - [Sub-paths](#sub-paths)
   - [Sub-domains](#sub-domains)
 - [Why does the code-server proxy strip `/proxy/<port>` from the request path?](#why-does-the-code-server-proxy-strip-proxyport-from-the-request-path)
+  - [Proxying to Create React App](#proxying-to-create-react-app)
 - [Multi-tenancy](#multi-tenancy)
 - [Docker in code-server container?](#docker-in-code-server-container)
 - [How can I disable telemetry?](#how-can-i-disable-telemetry)
@@ -226,25 +227,28 @@ However many people prefer the cleaner aesthetic of no trailing slashes. This co
 to the base path as you cannot use relative redirects correctly anymore. See the above
 link.
 
-For users who are ok with this tradeoff, pass `--proxy-path-passthrough` to code-server
-and the path will be passed as is.
+For users who are ok with this tradeoff, use `/absproxy` instead and the path will be
+passed as is. e.g. `/absproxy/3000/my-app-path`
 
-This is particularly a problem with the `start` script in create-react-app. See
+### Proxying to Create React App
+
+You must use `/absproxy/<port>` with create-react-app.
+See [#2565](https://github.com/cdr/code-server/issues/2565) and
 [#2222](https://github.com/cdr/code-server/issues/2222). You will need to inform
-create-react-app of the path at which you are serving via `homepage` field in your
-`package.json`. e.g. you'd add the following for the default CRA port:
+create-react-app of the path at which you are serving via `$PUBLIC_URL` and webpack
+via `$WDS_SOCKET_PATH`.
 
-```json
-  "homepage": "/proxy/3000",
+e.g.
+
+```sh
+PUBLIC_URL=/absproxy/3000 \
+  WDS_SOCKET_PATH=$PUBLIC_URL/sockjs-node \
+  BROWSER=none yarn start
 ```
 
-Then visit `https://my-code-server-address.io/proxy/3000` to see your app exposed through
+Then visit `https://my-code-server-address.io/absproxy/3000` to see your app exposed through
 code-server!
 
-Unfortunately `webpack-dev-server`'s websocket connections will not go through as it
-always uses `/sockjs-node`. So hot reloading will not work until the `create-react-app`
-team fix this bug.
-
 Highly recommend using the subdomain approach instead to avoid this class of issue.
 
 ## Multi-tenancy

src/node/proxy.ts

@@ -9,8 +9,7 @@ proxy.on("error", (error, _, res) => {
 })
 
 // Intercept the response to rewrite absolute redirects against the base path.
-// Is disabled when the request has no base path which means --proxy-path-passthrough has
-// been enabled.
+// Is disabled when the request has no base path which means /absproxy is in use.
 proxy.on("proxyRes", (res, req) => {
   if (res.headers.location && res.headers.location.startsWith("/") && (req as any).base) {
     res.headers.location = (req as any).base + res.headers.location