Preview deployments not working (v5), AUTH_REDIRECT_PROXY_URL

Environment

next: latest => 14.1.3
next-auth: beta => 5.0.0-beta.15
react: ^18.2.0 => 18.2.0

Reproduction URL

https://github.com/nextauthjs/next-auth/tree/main/apps/examples/nextjs

Describe the issue

As described in https://authjs.dev/getting-started/deployment#securing-a-preview-deployment, using AUTH_REDIRECT_PROXY_URL env variable should allow for preview deployments.

How to reproduce

Create new project using this template: https://github.com/nextauthjs/next-auth/tree/main/apps/examples/nextjs. Create new project on Vercel.

Set env variables:

AUTH_REDIRECT_PROXY_URL (Development, Preview) - https://next-auth-example-sepia.vercel.app/auth
AUTH_GITHUB_SECRET (Development, Preview, Production)
AUTH_GITHUB_ID (Development, Preview, Production)
AUTH_SECRET (Developmet, Preview, Production)

Add Callback URL to Github App Settings - https://next-auth-example-sepia.vercel.app/auth/callback/github.

Use one of the preview deployments:

https://next-auth-example-git-main-adisoncavani.vercel.app/

Try to "Sign In" using Github.

Error: http://localhost:3000/api/auth/callback/github?error=redirect_uri_mismatch&error_description=The+redirect_uri+MUST+match+the+registered+callback+URL+for+this+application.&error_uri=https%3A%2F%2Fdocs.github.com%2Fapps%2Fmanaging-oauth-apps%2Ftroubleshooting-authorization-request-errors%2F%23redirect-uri-mismatch

Expected behavior

Auth in preview deployments should work.

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nextauthjs / next-auth