doc: document TLS alpnProtocol and servername fields

Signed-off-by: Tim Perry <pimterry@gmail.com>

Author: pimterry

doc/api/tls.md

@@ -741,12 +741,9 @@ server. If `tlsSocket.authorized` is `false`, then `socket.authorizationError`
 is set to describe how authorization failed. Depending on the settings
 of the TLS server, unauthorized connections may still be accepted.
 
-The `tlsSocket.alpnProtocol` property is a string that contains the selected
-ALPN protocol. When ALPN has no selected protocol because the client or the
-server did not send an ALPN extension, `tlsSocket.alpnProtocol` equals `false`.
-
-The `tlsSocket.servername` property is a string containing the server name
-requested via SNI.
+The [`tls.TLSSocket.servername`][] and [`tls.TLSSocket.alpnProtocol`][]
+properties can be used to check which server name was requested, and which
+protocol was negotiated.
 
 ### Event: `'tlsClientError'`
 
@@ -1043,6 +1040,18 @@ Returns the bound `address`, the address `family` name, and `port` of the
 underlying socket as reported by the operating system:
 `{ port: 12346, family: 'IPv4', address: '127.0.0.1' }`.
 
+### `tlsSocket.alpnProtocol`
+
+<!-- YAML
+added: v6.0.0
+-->
+
+* Type: {string|boolean|null}
+
+The negotiated ALPN protocol. This is `null` before the handshake completes.
+Once the handshake completes, it settles as either the negotiated protocol
+name, or `false` if the peers did not negotiate an ALPN protocol.
+
 ### `tlsSocket.authorizationError`
 
 <!-- YAML
@@ -1570,6 +1579,18 @@ When running as the server, the socket will be destroyed with an error after
 For TLSv1.3, renegotiation cannot be initiated, it is not supported by the
 protocol.
 
+### `tlsSocket.servername`
+
+<!-- YAML
+added: v0.11.3
+-->
+
+* Type: {string|boolean|null}
+
+The SNI (Server Name Indication) host name associated with the socket. This is
+`null` before the handshake completes. Once the handshake completes it settles
+as either the host name string, or `false` if SNI was not used.
+
 ### `tlsSocket.setKeyCert(context)`
 
 <!-- YAML
@@ -2553,11 +2574,13 @@ added: v0.11.3
 [`tls.DEFAULT_MAX_VERSION`]: #tlsdefault_max_version
 [`tls.DEFAULT_MIN_VERSION`]: #tlsdefault_min_version
 [`tls.Server`]: #class-tlsserver
+[`tls.TLSSocket.alpnProtocol`]: #tlssocketalpnprotocol
 [`tls.TLSSocket.enableTrace()`]: #tlssocketenabletrace
 [`tls.TLSSocket.getPeerCertificate()`]: #tlssocketgetpeercertificatedetailed
 [`tls.TLSSocket.getProtocol()`]: #tlssocketgetprotocol
 [`tls.TLSSocket.getSession()`]: #tlssocketgetsession
 [`tls.TLSSocket.getTLSTicket()`]: #tlssocketgettlsticket
+[`tls.TLSSocket.servername`]: #tlssocketservername
 [`tls.TLSSocket`]: #class-tlstlssocket
 [`tls.connect()`]: #tlsconnectoptions-callback
 [`tls.createSecureContext()`]: #tlscreatesecurecontextoptions