Add compile-time option to enable X.509 CA callbacks
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 3a2fed5..ed8bafa 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1745,6 +1745,25 @@
//#define MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION
/**
+ * \def MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK
+ *
+ * If set, this enables the X.509 API `mbedtls_x509_crt_verify_with_cb()`
+ * and the SSL API `mbedtls_ssl_conf_ca_cb()` which allow users to configure
+ * the set of trusted certificates through a callback instead of a linked
+ * list.
+ *
+ * This is useful for example in environments where a large number of trusted
+ * certificates is present and storing them in a linked list isn't efficient
+ * enough, or when the set of trusted certificates changes frequently.
+ *
+ * See the documentation of `mbedtls_x509_crt_verify_with_cb()` and
+ * `mbedtls_ssl_conf_ca_cb()` for more information.
+ *
+ * Uncomment to enable trusted certificate callbacks.
+ */
+//#define MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK
+
+/**
* \def MBEDTLS_X509_CHECK_KEY_USAGE
*
* Enable verification of the keyUsage extension (CA and leaf certificates).