Docs: add identity-aware routing cross-links and access log fields (RFC-0055)

_gorouter_client_cert_oss.html.md.erb

@@ -6,6 +6,10 @@ You might change this behavior with the property `router.client_cert_validation`
 
 The behavior controlled by this property is global; it applies to all requests received by Gorouters so configured.
 
+<p class="note">
+Identity-aware routing uses a separate, <strong>per-domain</strong> mTLS mechanism that is configured through <code>router.domains</code> and enforces route policies independently of this global setting. For more information, see <a href="../deploying/cf-deployment/enable-identity-aware-routing.html">Enabling identity-aware routing</a>.
+</p>
+
 If Gorouter is the first point of TLS termination (your load balancer does not stop TLS, and passes the request through to
 Gorouter over TCP), consider the following:
 

instance-identity.html.md.erb

@@ -24,6 +24,8 @@ You can also install the Instance Identity CA certificate as a trusted system ce
 
 For information about how developers can use the Instance Identity credentials in apps on <%= vars.app_runtime_abbr %>, see [Using Instance Identity Credentials](../devguide/deploy-apps/instance-identity.html).
 
+The Instance Identity CA is also used by the Gorouter for per-domain mutual TLS (mTLS). For information about enabling this feature, see [Enabling identity-aware routing](../deploying/cf-deployment/enable-identity-aware-routing.html).
+
 
 ## <a id="configuring"></a> Configuring Instance Identity validity period
 

routing-index.html.md.erb

@@ -20,3 +20,4 @@ These topics are your source for information about managing routes and domains i
 * [Securing traffic into <%= vars.app_runtime_abbr %>](securing-traffic.html)
 * [Enabling and configuring TCP routing](enabling-tcp-routing.html)
 * [Configuring HTTP/2 support](supporting-http2.html)
+* [Enabling identity-aware routing](../deploying/cf-deployment/enable-identity-aware-routing.html)

troubleshooting-router-error-responses.html.md.erb

@@ -173,6 +173,16 @@ When Gorouter is configured to log additional request attempt details, the follo
 * `TLS Time` is the time spent during TLS handshake with the backend.
 * `Backend Time` is the time spent waiting on the backend to respond to the request.
 
+When identity-aware routing is enabled on a domain, the Gorouter records additional fields for each request. These fields appear in `<Extra Headers>` in the access log format above and show `-` when the request did not go through an identity-aware domain:
+
+* `tls_sni` is the TLS Server Name Indication (SNI) value the caller requested.
+* `caller_cf_app` is the caller's app GUID, extracted from the validated client certificate.
+* `caller_cf_space` is the caller's space GUID.
+* `caller_cf_org` is the caller's org GUID.
+* `route_policy` is the route-policy rule that matched the request, for example `cf:app:<app-guid>`. It is `-` when no rule matched or enforcement is disabled.
+
+For more information about identity-aware routing and how these fields are used for observability, see [Identity-aware routing](../concepts/identity-aware-routing.html).
+
 ## <a id="gorouter"></a>Diagnose Gorouter errors
 
 This section describes the basic structure of Gorouter logs and how to diagnose Gorouter errors.