document new TLS connection failure logging (#1578)

Update the mTLS Enforcement Mode documentation to mention that the
reject_connection mode will now enable TLS connection failure logging.
Tweak the formatting for this section of the docs.

Author: kenjenkins

content/docs/reference/downstream-mtls-settings.mdx

@@ -168,11 +168,13 @@ The Ingress Controller does not support these settings.
 
    This matches the default behavior of many popular reverse proxies, such as Apache httpd and Caddy.
 
-   Note that in this mode, client certificates will be required even for internal Pomerium routes, such as the authenticate URL (if using the self-hosted authenticate service) and the /.pomerium/ page (the page showing details of a user's current login session). In particular, any upstream services that perform [JWT verification](/docs/capabilities/getting-users-identity) will not be able to access the default [JWKS endpoint](/docs/reference/signing-key#how-to-use-signing-key). You may need to host your own JWKS endpoint, or provide some other means of distributing the JWT verification key(s).
+   Note that this mode also:
 
-   This mode also adds a requirement that any configured [**CRL**](#crl) is valid only between its `thisUpdate` and `nextUpdate` timestamps. _If an invalid CRL is provided for a certain CA, no certificates issued by that CA will be allowed._
+   - Requires client certificates even for internal Pomerium routes, such as the authenticate URL (if using the self-hosted authenticate service) and the /.pomerium/ page (the page showing details of a user's current login session). In particular, any upstream services that perform [JWT verification](/docs/capabilities/getting-users-identity) will not be able to access the default [JWKS endpoint](/docs/reference/signing-key#how-to-use-signing-key). You may need to host your own JWKS endpoint, or provide some other means of distributing the JWT verification key(s).
 
-   Also note that in this mode, requests without a trusted client certificate will never reach the Pomerium authorize service, and so no record of these requests will be logged.
+   - Adds a requirement that any configured [**CRL**](#crl) is valid only between its `thisUpdate` and `nextUpdate` timestamps. _If an invalid CRL is provided for a certain CA, no certificates issued by that CA will be allowed._
+
+   - Enables TLS connection failure logging. Any connection attempt that fails during the TLS handshake will be logged by the proxy service with the message `"listener connection failure"`. The log entry will include the client IP address, server hostname, and client certificate info (if a client certificate was presented), so you can monitor rejected connections. (Otherwise, when a connection is rejected due to mTLS requirements, the client would never have the opportunity to make any requests, and so there would be no entries in the [access log](/docs/reference/access-log-fields#access-log-behavior) or [authorize log](/docs/capabilities/audit-logs).)
 
 ### How to configure {#enforcement-mode-how-to-configure}