feat(asio): Add mbedtls specific APIs to use TLS stack specific features

Use mbedtls specific API to configure hostname for verification

Author: david-cermak

components/asio/examples/ssl_client_server/main/asio_ssl_main.cpp

@@ -17,6 +17,8 @@
 #include "asio/ssl.hpp"
 #include "asio/buffer.hpp"
 #include "esp_pthread.h"
+// allows for direct access to mbedtls specifics
+#include "asio/ssl/mbedtls_specific.hpp"
 
 extern const unsigned char server_pem_start[] asm("_binary_srv_crt_start");
 extern const unsigned char server_pem_end[]   asm("_binary_srv_crt_end");
@@ -217,6 +219,7 @@ void ssl_server_thread()
     io_context.run();
 }
 
+
 void ssl_client_thread()
 {
     asio::io_context io_context;
@@ -229,6 +232,11 @@ void ssl_client_thread()
     asio::ssl::context ctx(asio::ssl::context::tls_client);
 #if CONFIG_EXAMPLE_CLIENT_VERIFY_PEER
     ctx.add_certificate_authority(cert_chain);
+    // mbedtls (from 3.6.3) requires hostname to be set when performing TLS handshake with verify-peer option
+    // asio::ssl allows for name verification using verification callback, i.e. socket_.set_verify_callback(asio::ssl::host_name_verification()),
+    // - which is not supported in Espressif ASIO port yet.
+    // Therefore we provide a way to directly use mbedtls API and here we just configure the expected hostname to verify
+    asio::ssl::mbedtls::set_hostname(ctx.native_handle(), server_ip);
 #endif // CONFIG_EXAMPLE_CLIENT_VERIFY_PEER
 
     Client c(io_context, ctx, endpoints);

components/asio/port/include/asio/ssl/mbedtls_specific.hpp

@@ -0,0 +1,29 @@
+//
+// SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+//
+// SPDX-License-Identifier: BSL-1.0
+//
+
+#pragma once
+
+#include "asio/ssl/context_base.hpp"
+#include "asio/ssl/context.hpp"
+#include "asio/ssl/detail/openssl_types.hpp"
+
+namespace asio {
+namespace ssl {
+namespace mbedtls {
+
+/**
+ * @brief Configures specific hostname to be used in peer verification
+ *
+ * @param handle asio::ssl context handle type
+ * @param name hostname to be verified (std::string ownership will be moved to ssl::context)
+ *
+ * @return true on success
+ */
+bool set_hostname(asio::ssl::context::native_handle_type handle, std::string name);
+
+};
+};
+} // namespace asio::ssl::mbedtls

components/asio/port/mbedtls/include/mbedtls_context.hpp

@@ -1,5 +1,5 @@
 //
-// SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+// SPDX-FileCopyrightText: 2021-2025 Espressif Systems (Shanghai) CO LTD
 //
 // SPDX-License-Identifier: BSL-1.0
 //
@@ -52,6 +52,12 @@ class context {
         return nullptr;
     }
 
+    bool set_hostname(std::string hostname)
+    {
+        hostname_ = std::move(hostname);
+        return true;
+    }
+
     std::size_t size(container c) const
     {
         switch (c) {
@@ -70,6 +76,7 @@ class context {
     const_buffer cert_chain_;
     const_buffer private_key_;
     const_buffer ca_cert_;
+    std::string hostname_;
 };
 
 /**

components/asio/port/mbedtls/include/mbedtls_engine.hpp

@@ -1,5 +1,5 @@
 //
-// SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+// SPDX-FileCopyrightText: 2021-2025 Espressif Systems (Shanghai) CO LTD
 //
 // SPDX-License-Identifier: BSL-1.0
 //
@@ -16,6 +16,11 @@ namespace asio {
 namespace ssl {
 namespace mbedtls {
 
+bool set_hostname(asio::ssl::context::native_handle_type handle, std::string name)
+{
+    return handle->get()->set_hostname(std::move(name));
+}
+
 const char *error_message(int error_code)
 {
     static char error_buf[100];
@@ -25,7 +30,7 @@ const char *error_message(int error_code)
 
 void throw_alloc_failure(const char *location)
 {
-    asio::error_code ec( MBEDTLS_ERR_SSL_ALLOC_FAILED, asio::error::get_mbedtls_category());
+    asio::error_code ec(MBEDTLS_ERR_SSL_ALLOC_FAILED, asio::error::get_mbedtls_category());
     asio::detail::throw_error(ec, location);
 }
 
@@ -269,6 +274,16 @@ class engine {
             } else {
                 mbedtls_ssl_conf_ca_chain(&conf_, nullptr, nullptr);
             }
+
+            // Configure hostname before handshake if users pre-configured any
+            // use NULL if not set (to preserve the default behaviour of mbedtls < v3.6.3)
+            const char* hostname = !ctx->hostname_.empty() ? ctx->hostname_.c_str() : NULL;
+            ret = mbedtls_ssl_set_hostname(&ssl_, hostname);
+            if (ret < 0) {
+                print_error("mbedtls_ssl_set_hostname", ret);
+                return false;
+            }
+
             ret = mbedtls_ssl_setup(&ssl_, &conf_);
             if (ret) {
                 print_error("mbedtls_ssl_setup", ret);