Config: Added [allowed_keys] section for client public key authorization on server

- Added CFG_ALLOWED_KEY struct with binary key storage (64 bytes) for fast memcmp comparison
- Implemented parsing of [allowed_keys] section with allow_all flag and per-key entries
- Added key validation in etcp_connections.c server handler (errorcode=8 for rejected keys)
- Default behavior: deny all if [allowed_keys] section is missing or allow_all=0 with no keys
- Added proper memory cleanup and debug logging for allowed_keys configuration
- Updated all test configs to include [allowed_keys] allow_all=1 for backward compatibility

src/config_parser.h

@@ -5,6 +5,7 @@
 #include <stdint.h>
 #include <stddef.h>
 #include "../lib/platform_compat.h"
+#include "secure_channel.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -72,6 +73,11 @@ struct CFG_CONTROL_ALLOW {
     uint32_t netmask;  // netmask in host byte order (e.g. 0xffffff00 for /24)
 };
 
+struct CFG_ALLOWED_KEY {
+    uint8_t key_bin[SC_PUBKEY_SIZE];  // public key in binary (64 bytes)
+    struct CFG_ALLOWED_KEY *next;
+};
+
 struct global_config {
     char name[16];                    // Instance name
     char my_private_key_hex[MAX_KEY_LEN];
@@ -110,6 +116,11 @@ struct global_config {
     // Control server configuration ([control] section)
     struct CFG_CONTROL_ALLOW *control_allows;
     int control_allow_count;
+
+    // Allowed keys configuration ([allowed_keys] section)
+    struct CFG_ALLOWED_KEY *allowed_keys;
+    int allowed_keys_count;
+    int allowed_keys_allow_all;
 };
 
 struct utun_config {