SSL: $ssl_curve (ticket #2135). The variable contains a negotiated curve used for the handshake key exchange process. Known curves are listed by their names, unknown ones are shown in hex. Note that for resumed sessions in TLSv1.2 and older protocols, $ssl_curve contains the curve used during the initial handshake, while in TLSv1.3 it contains the curve used during the session resumption (see the SSL_get_negotiated_group manual page for details). The variable is only meaningful when using OpenSSL 3.0 and above. With older versions the variable is empty.

--- a/src/stream/ngx_stream_ssl_module.c
+++ b/src/stream/ngx_stream_ssl_module.c
@@ -269,6 +269,9 @@ static ngx_stream_variable_t  ngx_stream
     { ngx_string("ssl_ciphers"), NULL, ngx_stream_ssl_variable,
       (uintptr_t) ngx_ssl_get_ciphers, NGX_STREAM_VAR_CHANGEABLE, 0 },
 
+    { ngx_string("ssl_curve"), NULL, ngx_stream_ssl_variable,
+      (uintptr_t) ngx_ssl_get_curve, NGX_STREAM_VAR_CHANGEABLE, 0 },
+
     { ngx_string("ssl_curves"), NULL, ngx_stream_ssl_variable,
       (uintptr_t) ngx_ssl_get_curves, NGX_STREAM_VAR_CHANGEABLE, 0 },