Upstream: proxy_ssl_name and proxy_ssl_server_name directives.

These directives allow to switch on Server Name Indication (SNI) while
connecting to upstream servers.

By default, proxy_ssl_server_name is currently off (that is, no SNI) and
proxy_ssl_name is set to a host used in the proxy_pass directive.

src/http/modules/ngx_http_proxy_module.c

diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index 9e2cf61..7774f0f 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -553,6 +553,20 @@
       offsetof(ngx_http_proxy_loc_conf_t, ssl_ciphers),
       NULL },
 
+    { ngx_string("proxy_ssl_name"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
+      ngx_http_set_complex_value_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_proxy_loc_conf_t, upstream.ssl_name),
+      NULL },
+
+    { ngx_string("proxy_ssl_server_name"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_proxy_loc_conf_t, upstream.ssl_server_name),
+      NULL },
+
 #endif
 
       ngx_null_command
@@ -2390,6 +2404,7 @@
      *     conf->upstream.location = NULL;
      *     conf->upstream.store_lengths = NULL;
      *     conf->upstream.store_values = NULL;
+     *     conf->upstream.ssl_name = NULL;
      *
      *     conf->method = { 0, NULL };
      *     conf->headers_source = NULL;
@@ -2441,8 +2456,10 @@
     conf->upstream.pass_headers = NGX_CONF_UNSET_PTR;
 
     conf->upstream.intercept_errors = NGX_CONF_UNSET;
+
 #if (NGX_HTTP_SSL)
     conf->upstream.ssl_session_reuse = NGX_CONF_UNSET;
+    conf->upstream.ssl_server_name = NGX_CONF_UNSET;
 #endif
 
     /* "proxy_cyclic_temp_file" is disabled */
@@ -2714,6 +2731,7 @@
                               prev->upstream.intercept_errors, 0);
 
 #if (NGX_HTTP_SSL)
+
     ngx_conf_merge_value(conf->upstream.ssl_session_reuse,
                               prev->upstream.ssl_session_reuse, 1);
 
@@ -2725,9 +2743,17 @@
     ngx_conf_merge_str_value(conf->ssl_ciphers, prev->ssl_ciphers,
                              "DEFAULT");
 
+    if (conf->upstream.ssl_name == NULL) {
+        conf->upstream.ssl_name = prev->upstream.ssl_name;
+    }
+
+    ngx_conf_merge_value(conf->upstream.ssl_server_name,
+                              prev->upstream.ssl_server_name, 0);
+
     if (conf->ssl && ngx_http_proxy_set_ssl(cf, conf) != NGX_OK) {
         return NGX_CONF_ERROR;
     }
+
 #endif
 
     ngx_conf_merge_value(conf->redirect, prev->redirect, 1);