SSL: support for TLSv1.3 early data with BoringSSL.

Early data AKA 0-RTT mode is enabled as long as "ssl_early_data on" is
specified in the configuration (default is off).

The $ssl_early_data variable evaluates to "1" if the SSL handshake
isn't yet completed, and can be used to set the Early-Data header as
per draft-ietf-httpbis-replay-04.

src/event/ngx_event_openssl.c

@@ -1168,6 +1168,29 @@ ngx_ssl_ecdh_curve(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *name)
 }
 
 
+ngx_int_t
+ngx_ssl_early_data(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_uint_t enable)
+{
+    if (!enable) {
+        return NGX_OK;
+    }
+
+#ifdef SSL_ERROR_EARLY_DATA_REJECTED
+
+    /* BoringSSL */
+
+    SSL_CTX_set_early_data_enabled(ssl->ctx, 1);
+
+#else
+    ngx_log_error(NGX_LOG_WARN, ssl->log, 0,
+                  "\"ssl_early_data\" is not supported on this platform, "
+                  "ignored");
+#endif
+
+    return NGX_OK;
+}
+
+
 ngx_int_t
 ngx_ssl_client_session_cache(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_uint_t enable)
 {
@@ -3623,6 +3646,21 @@ ngx_ssl_get_session_reused(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
 }
 
 
+ngx_int_t
+ngx_ssl_get_early_data(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
+{
+    s->len = 0;
+
+#ifdef SSL_ERROR_EARLY_DATA_REJECTED
+    if (SSL_in_early_data(c->ssl->connection)) {
+        ngx_str_set(s, "1");
+    }
+#endif
+
+    return NGX_OK;
+}
+
+
 ngx_int_t
 ngx_ssl_get_server_name(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
 {

src/event/ngx_event_openssl.h

@@ -171,6 +171,8 @@ RSA *ngx_ssl_rsa512_key_callback(ngx_ssl_conn_t *ssl_conn, int is_export,
 ngx_array_t *ngx_ssl_read_password_file(ngx_conf_t *cf, ngx_str_t *file);
 ngx_int_t ngx_ssl_dhparam(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *file);
 ngx_int_t ngx_ssl_ecdh_curve(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *name);
+ngx_int_t ngx_ssl_early_data(ngx_conf_t *cf, ngx_ssl_t *ssl,
+    ngx_uint_t enable);
 ngx_int_t ngx_ssl_client_session_cache(ngx_conf_t *cf, ngx_ssl_t *ssl,
     ngx_uint_t enable);
 ngx_int_t ngx_ssl_session_cache(ngx_ssl_t *ssl, ngx_str_t *sess_ctx,
@@ -213,6 +215,8 @@ ngx_int_t ngx_ssl_get_session_id(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
 ngx_int_t ngx_ssl_get_session_reused(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
+ngx_int_t ngx_ssl_get_early_data(ngx_connection_t *c, ngx_pool_t *pool,
+    ngx_str_t *s);
 ngx_int_t ngx_ssl_get_server_name(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
 ngx_int_t ngx_ssl_get_raw_certificate(ngx_connection_t *c, ngx_pool_t *pool,

src/http/modules/ngx_http_ssl_module.c

@@ -239,6 +239,13 @@ static ngx_command_t  ngx_http_ssl_commands[] = {
       offsetof(ngx_http_ssl_srv_conf_t, stapling_verify),
       NULL },
 
+    { ngx_string("ssl_early_data"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_SRV_CONF_OFFSET,
+      offsetof(ngx_http_ssl_srv_conf_t, early_data),
+      NULL },
+
       ngx_null_command
 };
 
@@ -294,6 +301,10 @@ static ngx_http_variable_t  ngx_http_ssl_vars[] = {
     { ngx_string("ssl_session_reused"), NULL, ngx_http_ssl_variable,
       (uintptr_t) ngx_ssl_get_session_reused, NGX_HTTP_VAR_CHANGEABLE, 0 },
 
+    { ngx_string("ssl_early_data"), NULL, ngx_http_ssl_variable,
+      (uintptr_t) ngx_ssl_get_early_data,
+      NGX_HTTP_VAR_CHANGEABLE|NGX_HTTP_VAR_NOCACHEABLE, 0 },
+
     { ngx_string("ssl_server_name"), NULL, ngx_http_ssl_variable,
       (uintptr_t) ngx_ssl_get_server_name, NGX_HTTP_VAR_CHANGEABLE, 0 },
 
@@ -552,6 +563,7 @@ ngx_http_ssl_create_srv_conf(ngx_conf_t *cf)
 
     sscf->enable = NGX_CONF_UNSET;
     sscf->prefer_server_ciphers = NGX_CONF_UNSET;
+    sscf->early_data = NGX_CONF_UNSET;
     sscf->buffer_size = NGX_CONF_UNSET_SIZE;
     sscf->verify = NGX_CONF_UNSET_UINT;
     sscf->verify_depth = NGX_CONF_UNSET_UINT;
@@ -594,6 +606,8 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_value(conf->prefer_server_ciphers,
                          prev->prefer_server_ciphers, 0);
 
+    ngx_conf_merge_value(conf->early_data, prev->early_data, 0);
+
     ngx_conf_merge_bitmask_value(conf->protocols, prev->protocols,
                          (NGX_CONF_BITMASK_SET|NGX_SSL_TLSv1
                           |NGX_SSL_TLSv1_1|NGX_SSL_TLSv1_2));
@@ -809,6 +823,10 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
 
     }
 
+    if (ngx_ssl_early_data(cf, &conf->ssl, conf->early_data) != NGX_OK) {
+        return NGX_CONF_ERROR;
+    }
+
     return NGX_CONF_OK;
 }
 

src/http/modules/ngx_http_ssl_module.h

@@ -20,6 +20,7 @@ typedef struct {
     ngx_ssl_t                       ssl;
 
     ngx_flag_t                      prefer_server_ciphers;
+    ngx_flag_t                      early_data;
 
     ngx_uint_t                      protocols;