docs: add proper example

Author: falko17

example/dcaf_example.dart

@@ -9,17 +9,83 @@
  * SPDX-License-Identifier: MIT OR Apache-2.0
  */
 
-import 'dart:convert';
+import 'package:cbor/cbor.dart';
 import 'package:dcaf/dcaf.dart';
 
 void main() {
+  // Creating and (de)serializing a Creation Hint:
+  final scope = TextScope("rTempC");
+  final hint = AuthServerRequestCreationHint(
+      authorizationServer: "coaps://as.example.com/token",
+      audience: "coaps://rs.example.com",
+      scope: scope,
+      clientNonce: [0xe0, 0xa1, 0x56, 0xbb, 0x3f]);
+  final List<int> serializedHint = hint.serialize();
+
+  assert(AuthServerRequestCreationHint.fromSerialized(serializedHint) == hint);
+  // Creating and (de)serializing an Access Token Request:
   final request = AccessTokenRequest(
       clientId: "myclient",
       audience: "valve242",
       scope: TextScope("read"),
       reqCnf: KeyId([0xDC, 0xAF]));
-  final List<int> serialized = request.serialize();
-  assert(AccessTokenRequest.fromSerialized(serialized) == request);
+  final List<int> serializedRequest = request.serialize();
+  assert(AccessTokenRequest.fromSerialized(serializedRequest) == request);
+
+  // Creating and (de)serializing an Access Token Response
+  // which is represented in CBOR diagnostic notation like this...
+  // {
+  //   "access_token" : b64'SlAV32hkKG ...
+  //    (remainder of CWT omitted for brevity;
+  //    CWT contains COSE_Key in the "cnf" claim)',
+  //   "ace_profile" : "coap_dtls",
+  //   "expires_in" : "3600",
+  //   "cnf" : {
+  //     "COSE_Key" : {
+  //       "kty" : "Symmetric",
+  //       "kid" : b64'39Gqlw',
+  //       "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
+  //     }
+  //   }
+  // }
+  //
+  // ...would look like this:
 
-  // TODO(falko17): Further examples, including responses, creation hints, etc.
+  final key = CoseKey(keyType: KeyType.symmetric, keyId: [
+    0xDF,
+    0xD1,
+    0xAA,
+    0x97
+  ], parameters: {
+    // field "k" (the key itself)
+    -1: CborBytes([
+      0x84,
+      0x9b,
+      0x57,
+      0x86,
+      0x45,
+      0x7c,
+      0x14,
+      0x91,
+      0xbe,
+      0x3a,
+      0x76,
+      0xdc,
+      0xea,
+      0x6c,
+      0x42,
+      0x71,
+      0x08
+    ])
+  });
+  final response = AccessTokenResponse(
+      // NOTE: This is not what the access token is really supposed to be!
+      // In an actual implementation, it should contain a properly
+      // signed/encrypted CWT with the `key` defined above in its `cnf` claim!
+      accessToken: [0xDC, 0xAF],
+      aceProfile: AceProfile.coapDtls,
+      expiresIn: 3600,
+      cnf: PlainCoseKey(key));
+  final serialized = response.serialize();
+  assert(AccessTokenResponse.fromSerialized(serialized) == response);
 }