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Add documentation for trusted_proxies_strict (#346)

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Co-authored-by: Francis Lavoie <lavofr@gmail.com>
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Nebez Briefkani 2024-04-23 09:15:28 -07:00 • committed by Francis Lavoie
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src/docs/markdown/caddyfile/options.md
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@ -827,7 +827,7 @@ Also included is the [`proxy_protocol`](/docs/json/apps/http/servers/listener_wr
Allows configuring IP ranges (CIDRs) of proxy servers from which requests should be trusted. By default, no proxies are trusted. Allows configuring IP ranges (CIDRs) of proxy servers from which requests should be trusted. By default, no proxies are trusted.
Enabling this causes trusted requests to have the _real_ client IP parsed from HTTP headers (by default, `X-Forwarded-For`; see [`client_ip_headers`](#client-ip-headers) to configure other headers). If trusted, the client IP is added to [access logs](/docs/caddyfile/directives/log), is available as a `{client_ip}` [placeholder](/docs/caddyfile/concepts#placeholders), and allows the use of the [`client_ip` matcher](/docs/caddyfile/matchers#client-ip). If the request is not from a trusted proxy, then the client IP is set to the remote IP address of the direct incoming connection. Enabling this causes trusted requests to have the _real_ client IP parsed from HTTP headers (by default, `X-Forwarded-For`; see [`client_ip_headers`](#client-ip-headers) to configure other headers). If trusted, the client IP is added to [access logs](/docs/caddyfile/directives/log), is available as a `{client_ip}` [placeholder](/docs/caddyfile/concepts#placeholders), and allows the use of the [`client_ip` matcher](/docs/caddyfile/matchers#client-ip). If the request is not from a trusted proxy, then the client IP is set to the remote IP address of the direct incoming connection. By default, the IPs in headers are parsed left-to-right. See [`trusted_proxies_strict`](#trusted-proxies-strict) to alter this behaviour.
Some matchers or handlers may use the trust status of the request to make decisions. For example, if trusted, the [`reverse_proxy`](/docs/caddyfile/directives/reverse_proxy#defaults) handler will proxy and augment the sensitive `X-Forwarded-*` request headers. Some matchers or handlers may use the trust status of the request to make decisions. For example, if trusted, the [`reverse_proxy`](/docs/caddyfile/directives/reverse_proxy#defaults) handler will proxy and augment the sensitive `X-Forwarded-*` request headers.
@ -856,6 +856,27 @@ Here's a complete example, trusting an example IPv4 range and an IPv6 range:
} }
``` ```
##### `trusted_proxies_strict`
When [`trusted_proxies`](#trusted-proxies) is enabled, the IPs in the headers (configured by [`client_ip_headers`](#client-ip-headers)) are parsed from left-to-right by default. The first untrusted IP address found becomes the real client address. Since v2.8, you can opt-in to right-to-left parsing of these headers with `trusted_proxies_strict`. By default, this option is disabled for backwards compatibility.
Upstream proxies such as HAProxy, CloudFlare, AWS ALB, CloudFront, etc. will append each new connecting remote address to the right of `X-Forwarded-For`. It is recommended to enable `trusted_proxies_strict` when working with these, as the left-most IP address may be spoofed by the client.
```caddy
{
servers {
trusted_proxies static private_ranges
trusted_proxies_strict
}
}
```
<aside class="tip">
Specifically in the case of AWS ALB, you will certainly want to enable this option. [Per their documentation](https://docs.aws.amazon.com/elasticloadbalancing/latest/application/x-forwarded-headers.html#w227aac13c27b9c15) you can only identify the real client IP by setting XFF mode to `append`. This IP will be appended to the right of `X-Forwarded-For` and can only be safely extracted via `trusted_proxies_strict`.
</aside>
##### `client_ip_headers` ##### `client_ip_headers`