fix: Frontend API proxy example for Next.js

[brkalow]

🔎 Previews:

• https://clerk.com/docs/pr/2248/advanced-usage/using-proxies

What does this solve?

• The proxy middleware example does not work properly as the proxy logic is not executed until clerkMiddleware() authenticates the request. This is unnecessary and causes issues in the handshake flow.

What changed?

The implementation has been improved to guarantee that proxy routes are always checked and handled before the Clerk middleware executes. This execution order is critical because it ensures that requests to the proxy path (__clerk) are correctly intercepted and routed to Clerk's Frontend API before any authentication middleware runs, preventing potential conflicts in request handling.

Checklist

• I have clicked on "Files changed" and performed a thorough self-review
• All existing checks pass

[github-actions]

Hey, here’s your docs preview: https://clerk.com/docs/pr/2248

[alexisintech]

😸💖

[royanger]

It might be worth linking to this from the clerkMiddleware doc. Maybe from

clerk-docs/docs/_partials/clerk-middleware-options.mdx

Lines 53 to 54 in 8a52740

	- `proxyUrl?`
	- `string`

[royanger]

Hey @brkalow, I was going to create a linear but with this PR still open, did you want to make the following fix in the warning callout?

If your application already uses a CNAME subdomain that is required for deploying with Clerk, then you must proxy the Frontend API using a different subdomain.

The last part should read '...you must proxy the Frontend API using a path on your domain' or something along those lines.

I can do a separate ticket if you want.

[brkalow]

@royanger feel free to push up directly to this branch!