Warn capath is not supported for websockets

libwebsockets doesn't provide an option to provide a `capath`, ie
a directory that contains multiple certificates.
( warmcat/libwebsockets#3276 )

To avoid confusion, explicitly state that it's not supported for
websockets in the doc for mosquitto.conf, and add a warning if option is
provided while `capath` is not provided.

man/mosquitto.conf.5.xml

@@ -1326,6 +1326,7 @@ log_timestamp_format %Y-%m-%dT%H:%M:%S
 							"openssl rehash <path to capath>" each time
 							you add/remove a certificate.
 						</para>
+						<para><option>capath</option> is not supported for websockets.</para>
 					</listitem>
 				</varlistentry>
 				<varlistentry>

mosquitto.conf

@@ -359,6 +359,7 @@
 # containing the CA certificates. For capath to work correctly, the
 # certificate files must have ".crt" as the file ending and you must run
 # "openssl rehash <path to capath>" each time you add/remove a certificate.
+# capath is not supported for websockets.
 #cafile
 #capath
 

src/websockets.c

@@ -698,7 +698,12 @@ void mosq_websockets_init(struct mosquitto__listener *listener, const struct mos
 	info.gid = -1;
 	info.uid = -1;
 #ifdef WITH_TLS
-	info.ssl_ca_filepath = listener->cafile;
+	if(listener->cafile){
+		info.ssl_ca_filepath = listener->cafile;
+	}
+	else if(listener->capath){
+		log__printf(NULL, MOSQ_LOG_WARNING, "Warning: CA path option is not supported for websockets");
+	}
 	info.ssl_cert_filepath = listener->certfile;
 	info.ssl_private_key_filepath = listener->keyfile;
 	info.ssl_cipher_list = listener->ciphers;