SSL: workaround for session timeout handling with TLSv1.3.

OpenSSL with TLSv1.3 updates the session creation time on session
resumption and keeps the session timeout unmodified, making it possible
to maintain the session forever, bypassing client certificate expiration
and revocation.  To make sure session timeouts are actually used, we
now update the session creation time and reduce the session timeout
accordingly.

BoringSSL with TLSv1.3 ignores configured session timeouts and uses a
hardcoded timeout instead, 7 days.  So we update session timeout to
the configured value as soon as a session is created.

src/event/ngx_event_openssl.c

@@ -1084,6 +1084,53 @@ ngx_ssl_info_callback(const ngx_ssl_conn_t *ssl_conn, int where, int ret)
         }
     }
 
+#endif
+
+#ifdef TLS1_3_VERSION
+
+    if ((where & SSL_CB_ACCEPT_LOOP) == SSL_CB_ACCEPT_LOOP
+        && SSL_version(ssl_conn) == TLS1_3_VERSION)
+    {
+        time_t        now, time, timeout, conf_timeout;
+        SSL_SESSION  *sess;
+
+        /*
+         * OpenSSL with TLSv1.3 updates the session creation time on
+         * session resumption and keeps the session timeout unmodified,
+         * making it possible to maintain the session forever, bypassing
+         * client certificate expiration and revocation.  To make sure
+         * session timeouts are actually used, we now update the session
+         * creation time and reduce the session timeout accordingly.
+         *
+         * BoringSSL with TLSv1.3 ignores configured session timeouts
+         * and uses a hardcoded timeout instead, 7 days.  So we update
+         * session timeout to the configured value as soon as a session
+         * is created.
+         */
+
+        c = ngx_ssl_get_connection((ngx_ssl_conn_t *) ssl_conn);
+        sess = SSL_get0_session(ssl_conn);
+
+        if (!c->ssl->session_timeout_set && sess) {
+            c->ssl->session_timeout_set = 1;
+
+            now = ngx_time();
+            time = SSL_SESSION_get_time(sess);
+            timeout = SSL_SESSION_get_timeout(sess);
+            conf_timeout = SSL_CTX_get_timeout(c->ssl->session_ctx);
+
+            timeout = ngx_min(timeout, conf_timeout);
+
+            if (now - time >= timeout) {
+                SSL_SESSION_set1_id_context(sess, (unsigned char *) "", 0);
+
+            } else {
+                SSL_SESSION_set_time(sess, now);
+                SSL_SESSION_set_timeout(sess, timeout - (now - time));
+            }
+        }
+    }
+
 #endif
 
     if ((where & SSL_CB_ACCEPT_LOOP) == SSL_CB_ACCEPT_LOOP) {

src/event/ngx_event_openssl.h

@@ -114,6 +114,7 @@ struct ngx_ssl_connection_s {
     unsigned                    no_send_shutdown:1;
     unsigned                    shutdown_without_free:1;
     unsigned                    handshake_buffer_set:1;
+    unsigned                    session_timeout_set:1;
     unsigned                    try_early_data:1;
     unsigned                    in_early:1;
     unsigned                    in_ocsp:1;