feat(binding_coap): add support for PEM root certificates

lib/binding_coap.dart

@@ -10,6 +10,9 @@
 /// [spec link]: https://www.w3.org/TR/wot-binding-templates/
 library binding_coap;
 
+export "package:coap/coap.dart"
+    show Certificate, DerCertificate, PemCertificate;
+
 export "src/binding_coap/coap_client_factory.dart";
 export "src/binding_coap/coap_config.dart";
 export "src/binding_coap/coap_server.dart";

lib/src/binding_coap/coap_client.dart

@@ -5,7 +5,6 @@
 // SPDX-License-Identifier: BSD-3-Clause
 
 import "dart:async";
-import "dart:typed_data";
 
 import "package:coap/coap.dart" as coap;
 import "package:coap/config/coap_config_default.dart";
@@ -41,7 +40,7 @@ class _InternalCoapConfig extends CoapConfigDefault {
   final bool dtlsWithTrustedRoots;
 
   @override
-  final List<Uint8List> rootCertificates;
+  final List<coap.Certificate> rootCertificates;
 }
 
 coap.PskCredentialsCallback? _createPskCallback(

lib/src/binding_coap/coap_config.dart

@@ -4,8 +4,7 @@
 //
 // SPDX-License-Identifier: BSD-3-Clause
 
-import "dart:typed_data";
-
+import "package:coap/coap.dart";
 import "package:meta/meta.dart";
 
 /// Allows for configuring the behavior of CoAP clients and servers.
@@ -34,7 +33,7 @@ class CoapConfig {
   final String? dtlsCiphers;
 
   /// List of custom root certificates to use with OpenSSL.
-  final List<Uint8List> rootCertificates;
+  final List<Certificate> rootCertificates;
 
   /// The port number used by a client or server. Defaults to 5683.
   final int port;

pubspec.yaml

@@ -31,3 +31,9 @@ dependencies:
   typed_data: ^1.3.2
   uri: ^1.0.0
   uuid: ^4.2.1
+
+dependency_overrides:
+  coap:
+    git:
+      url: https://github.com/namib-project/coap
+      ref: dtls2-security-level