SSL: $ssl_sigalg, $ssl_client_sigalg.

Variables contain the IANA name of the signature scheme[1] used to sign
the TLS handshake.

Variables are only meaningful when using OpenSSL 3.5 and above, with older
versions they are empty.  Moreover, since this data isn't stored in a
serialized session, variables are only available for new sessions.

[1] https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml

Requested by willmafh.

src/event/ngx_event_openssl.c

@@ -5540,6 +5540,32 @@ ngx_ssl_get_curves(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
 }
 
 
+ngx_int_t
+ngx_ssl_get_sigalg(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
+{
+#ifdef SSL_get0_signature_name
+
+    const char  *name;
+
+    if (SSL_get0_signature_name(c->ssl->connection, &name)) {
+        s->len = ngx_strlen(name);
+        s->data = ngx_pnalloc(pool, s->len);
+        if (s->data == NULL) {
+            return NGX_ERROR;
+        }
+
+        ngx_memcpy(s->data, name, s->len);
+
+        return NGX_OK;
+    }
+
+#endif
+
+    s->len = 0;
+    return NGX_OK;
+}
+
+
 ngx_int_t
 ngx_ssl_get_session_id(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
 {
@@ -6285,6 +6311,32 @@ ngx_ssl_parse_time(
 }
 
 
+ngx_int_t
+ngx_ssl_get_client_sigalg(ngx_connection_t *c, ngx_pool_t *pool, ngx_str_t *s)
+{
+#ifdef SSL_get0_peer_signature_name
+
+    const char  *name;
+
+    if (SSL_get0_peer_signature_name(c->ssl->connection, &name)) {
+        s->len = ngx_strlen(name);
+        s->data = ngx_pnalloc(pool, s->len);
+        if (s->data == NULL) {
+            return NGX_ERROR;
+        }
+
+        ngx_memcpy(s->data, name, s->len);
+
+        return NGX_OK;
+    }
+
+#endif
+
+    s->len = 0;
+    return NGX_OK;
+}
+
+
 static void *
 ngx_openssl_create_conf(ngx_cycle_t *cycle)
 {

src/event/ngx_event_openssl.h

@@ -328,6 +328,8 @@ ngx_int_t ngx_ssl_get_curve(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
 ngx_int_t ngx_ssl_get_curves(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
+ngx_int_t ngx_ssl_get_sigalg(ngx_connection_t *c, ngx_pool_t *pool,
+    ngx_str_t *s);
 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,
@@ -364,6 +366,8 @@ ngx_int_t ngx_ssl_get_client_v_end(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
 ngx_int_t ngx_ssl_get_client_v_remain(ngx_connection_t *c, ngx_pool_t *pool,
     ngx_str_t *s);
+ngx_int_t ngx_ssl_get_client_sigalg(ngx_connection_t *c, ngx_pool_t *pool,
+    ngx_str_t *s);
 
 
 ngx_int_t ngx_ssl_handshake(ngx_connection_t *c);

src/http/modules/ngx_http_ssl_module.c

@@ -358,6 +358,9 @@ static ngx_http_variable_t  ngx_http_ssl_vars[] = {
     { ngx_string("ssl_curves"), NULL, ngx_http_ssl_variable,
       (uintptr_t) ngx_ssl_get_curves, NGX_HTTP_VAR_CHANGEABLE, 0 },
 
+    { ngx_string("ssl_sigalg"), NULL, ngx_http_ssl_variable,
+      (uintptr_t) ngx_ssl_get_sigalg, NGX_HTTP_VAR_CHANGEABLE, 0 },
+
     { ngx_string("ssl_session_id"), NULL, ngx_http_ssl_variable,
       (uintptr_t) ngx_ssl_get_session_id, NGX_HTTP_VAR_CHANGEABLE, 0 },
 
@@ -415,6 +418,9 @@ static ngx_http_variable_t  ngx_http_ssl_vars[] = {
     { ngx_string("ssl_client_v_remain"), NULL, ngx_http_ssl_variable,
       (uintptr_t) ngx_ssl_get_client_v_remain, NGX_HTTP_VAR_CHANGEABLE, 0 },
 
+    { ngx_string("ssl_client_sigalg"), NULL, ngx_http_ssl_variable,
+      (uintptr_t) ngx_ssl_get_client_sigalg, NGX_HTTP_VAR_CHANGEABLE, 0 },
+
       ngx_http_null_variable
 };
 

src/stream/ngx_stream_ssl_module.c

@@ -357,6 +357,9 @@ static ngx_stream_variable_t  ngx_stream_ssl_vars[] = {
     { ngx_string("ssl_curves"), NULL, ngx_stream_ssl_variable,
       (uintptr_t) ngx_ssl_get_curves, NGX_STREAM_VAR_CHANGEABLE, 0 },
 
+    { ngx_string("ssl_sigalg"), NULL, ngx_stream_ssl_variable,
+      (uintptr_t) ngx_ssl_get_sigalg, NGX_STREAM_VAR_CHANGEABLE, 0 },
+
     { ngx_string("ssl_session_id"), NULL, ngx_stream_ssl_variable,
       (uintptr_t) ngx_ssl_get_session_id, NGX_STREAM_VAR_CHANGEABLE, 0 },
 
@@ -404,6 +407,9 @@ static ngx_stream_variable_t  ngx_stream_ssl_vars[] = {
     { ngx_string("ssl_client_v_remain"), NULL, ngx_stream_ssl_variable,
       (uintptr_t) ngx_ssl_get_client_v_remain, NGX_STREAM_VAR_CHANGEABLE, 0 },
 
+    { ngx_string("ssl_client_sigalg"), NULL, ngx_stream_ssl_variable,
+      (uintptr_t) ngx_ssl_get_client_sigalg, NGX_STREAM_VAR_CHANGEABLE, 0 },
+
       ngx_stream_null_variable
 };