chore(docs): update Redirect Proxy related documentation to clarify s…

…upport for `form_post` providers (i.e. Apple) (#12309)

docs/pages/getting-started/deployment.mdx

@@ -49,6 +49,8 @@ This environment variable is mostly unnecessary with v5 as the host is inferred
 
 ### `AUTH_REDIRECT_PROXY_URL`
 
+> **_NOTE:_** Some providers (eg Apple) do not support [redirect proxy](https://github.com/nextauthjs/next-auth/blob/3ec06842682a31e53fceabca701a362abda1e7dd/packages/core/src/lib/utils/providers.ts#L48) usage.
+
 This environment variable is designed for advanced use-cases only, when using Auth.js as a proxy for preview deploys, for example. For more details, see the [securing preview deploys](#securing-a-preview-deployment) section below.
 
 ## Serverless
@@ -163,9 +165,11 @@ CMD ["node", "server.js"]
 
 ## Securing a preview deployment
 
+> **_NOTE:_** Some providers (eg Apple) do not support [redirect proxy](https://github.com/nextauthjs/next-auth/blob/3ec06842682a31e53fceabca701a362abda1e7dd/packages/core/src/lib/utils/providers.ts#L48) usage.
+
 Most OAuth providers cannot be configured with multiple callback URLs or using a wildcard.
 
-However, Auth.js **supports Preview deployments**, even **with OAuth providers**. The idea is to have one deployment which proxies authentication requests to the dynamic URLs of your main application. So you could have 1 stable deployment, like at `auth.company.com` where you would point all your OAuth provider's `callbackUrl`s, and this application would then, upon successful authentication, redirect the user back to the preview deploy URL, like `https://git-abc123-myapp.vercel.app`. Follow these steps to get started with securing preview deploys with Auth.js.
+However, Auth.js **supports Preview deployments**, even **with most OAuth providers**. The idea is to have one deployment which proxies authentication requests to the dynamic URLs of your main application. So you could have 1 stable deployment, like at `auth.company.com` where you would point all your OAuth provider's `callbackUrl`s, and this application would then, upon successful authentication, redirect the user back to the preview deploy URL, like `https://git-abc123-myapp.vercel.app`. Follow these steps to get started with securing preview deploys with Auth.js.
 
 1. Determine a stable deployment URL. For example, a deployment whose URL does not change between builds, for example. `auth.yourdomain.com` (using a subdomain is not a requirement, this can be the main site's URL too, for example.)
 2. In **both the preview and stable environment**, set `AUTH_REDIRECT_PROXY_URL` to that stable deployment URL, including the path from where Auth.js handles the routes. Eg.: (`https://auth.yourdomain.com/api/auth`). If the variable is not set in the stable environment, the proxy functionality will not be enabled!

docs/pages/getting-started/providers/apple.mdx

@@ -10,6 +10,8 @@ import { Code } from "@/components/Code"
 - Sign in with Apple [REST API](https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_rest_api)
 - [How to retrieve](https://developer.apple.com/documentation/sign_in_with_apple/sign_in_with_apple_rest_api/authenticating_users_with_sign_in_with_apple#3383773) the user's information from Apple ID servers
 
+> **_NOTE:_**  Apple currently does not support [RedirectProxyUrl](https://github.com/nextauthjs/next-auth/blob/3ec06842682a31e53fceabca701a362abda1e7dd/packages/core/src/lib/utils/providers.ts#L48) usage.
+
 ## Setup
 
 ### Callback URL