Add HTTP/3 Host header support for ModSecurity

ModSecurity cannot see the Host header in HTTP/3 requests because HTTP/3 uses the `:authority` pseudo-header, which nginx parses into `r->headers_in.server` but doesn't add to the headers list.

This commit:
- Adds `NGX_HTTP_VERSION_30` case to `http_version` switch
- Manually extracts Host from `r->headers_in.server` for HTTP/3 requests
- Adds Host header to ModSecurity transaction before processing other headers

Fixes #305 false positives from OWASP CRS rule 920280 (Missing Host Header) on HTTP/3 connections.

Tested with nginx 1.29.3 and ModSecurity 3.0.13.

Author: AMoo-Miki

src/ngx_http_modsecurity_rewrite.c

@@ -177,6 +177,11 @@ ngx_http_modsecurity_rewrite_handler(ngx_http_request_t *r)
             case NGX_HTTP_VERSION_20 :
                 http_version = "2.0";
                 break;
+#endif
+#if defined(nginx_version) && nginx_version >= 1025000
+            case NGX_HTTP_VERSION_30 :
+                http_version = "3.0";
+                break;
 #endif
             default :
                 http_version = ngx_str_to_char(r->http_protocol, r->pool);
@@ -212,9 +217,22 @@ ngx_http_modsecurity_rewrite_handler(ngx_http_request_t *r)
         }
 
         /**
-         * Since incoming request headers are already in place, lets send it to ModSecurity
-         *
+         * HTTP/3 uses :authority pseudo-header instead of Host header and nginx
+         * parses it into r->headers_in.server (see ngx_http_v3_request.c#L982)
+         * but doesn't add it to the headers list, so ModSecurity never sees it.
+         * We manually add Host header from r->headers_in.server for ModSecurity
+         * before processing the remaining headers.
          */
+        if (strcmp(http_version, "3.0") == 0 && r->headers_in.server.len > 0) {
+            dd("adding Host header from :authority: %.*s",
+               (int)r->headers_in.server.len, r->headers_in.server.data);
+
+            msc_add_n_request_header(ctx->modsec_transaction,
+                (const unsigned char *)"Host", 4,
+                (const unsigned char *)r->headers_in.server.data,
+                r->headers_in.server.len);
+        }
+
         ngx_list_part_t *part = &r->headers_in.headers.part;
         ngx_table_elt_t *data = part->elts;
         ngx_uint_t i = 0;