baiuu opened a new issue, #13742:
URL: https://github.com/apache/apisix/issues/13742
### Description
### Description
The `error-page` plugin currently has two limitations that make custom error
pages less useful in production:
**1. Limited status code coverage.** Only 404/500/502/503 are supported.
APISIX-generated 403 responses are common — auth plugin rejections (key-auth,
jwt-auth, etc.), ACL blocks, or custom serverless logic — but they cannot be
replaced with a custom page.
**2. Static body only.** The configured `body` is returned as a static
string. Operators typically want to embed request-scoped information into error
pages — most importantly the **request ID**, so that end users can report it
and administrators can correlate the error page with access/error logs.
### Proposal
**Part 1 — Support 403:**
- Add `error_403` to `metadata_schema` (same structure as existing entries)
- Lower the status threshold in `get_metadata` from `status < 404` to
`status < 400`; interception still requires an explicitly configured
`error_<status>` key, so behavior for unconfigured codes is unchanged
**Part 2 — Nginx variables in body:**
- Resolve variables via `core.utils.resolve_var` (the same mechanism used by
`response-rewrite` headers) before sending the response
- Resolution happens in `header_filter` so `Content-Length` is computed from
the **final rendered body** (avoids truncation/connection stalls)
- Supports `$var`, `${var}`, the `??` default-value operator, and `\$`
escaping
- Fail-open: on resolution failure, fall back to the original body and log a
warning
- Zero overhead for existing configurations (bodies without `$`
short-circuit before regex processing)
Example:
```json
{
"enable": true,
"error_403": {
"body": "<html><body><h1>403 Forbidden</h1><p>Request ID:
$apisix_request_id</p></body></html>",
"content_type": "text/html"
}
}
```
Both parts are backward compatible and independent of each other, but they
combine naturally — e.g. a custom 403 page showing `$apisix_request_id` for
troubleshooting auth rejections.
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