feat(backend): Allow reading proto and host for proxied requests from a custom header

[ItalyPaleAle]

Description

When Clerk is served behind a proxy, it uses the X-Forwarded-Proto and X-Forwarded-Host headers to determine the proto and host of the request, and redirect the client to the right place, as per docs.

However, we are dealing with a situation where because of other proxies in-between, we cannot leverage the X-Forwarded-Host header, and that makes Clerk not usable in this environment.

I am proposing adding two new environmental variables which allow overriding the name of the header that Clerk uses to perform lookups:

• CLERK_PROXY_FORWARDED_PROTO_HEADER
• CLERK_PROXY_FORWARDED_HOST_HEADER

Checklist

• [X] pnpm test runs as expected.
• [X] pnpm build runs as expected.
• N/A (If applicable) JSDoc comments have been added or updated for any package exports
• [ ] (If applicable) Documentation has been updated

Type of change

• [ ] 🐛 Bug fix
• [X] 🌟 New feature
• [ ] 🔨 Breaking change
• [ ] 📖 Refactoring / dependency upgrade / documentation
• [ ] other:

Summary by CodeRabbit

• New Features

  • Allow configuring which proxy headers are used to determine request protocol and host via environment settings, preserving default behavior for standard proxies.

• Tests

  • Added tests covering custom proxy header configurations to ensure correct origin detection across proxy setups.