feat(xep): Allow setting a tag when using Bind2

packages/moxxmpp/lib/src/xeps/xep_0386.dart

@@ -10,6 +10,9 @@ import 'package:moxxmpp/src/types/result.dart';
 class Bind2Negotiator extends Sasl2FeatureNegotiator {
   Bind2Negotiator() : super(0, false, bind2Xmlns, bind2Negotiator);
 
+  /// A tag to sent to the server when requesting Bind2.
+  String? tag;
+
   @override
   Future<Result<NegotiatorState, NegotiatorError>> negotiate(
     XMLNode nonza,
@@ -23,6 +26,13 @@ class Bind2Negotiator extends Sasl2FeatureNegotiator {
       XMLNode.xmlns(
         tag: 'bind',
         xmlns: bind2Xmlns,
+        children: [
+          if (tag != null)
+            XMLNode(
+              tag: 'tag',
+              text: tag,
+            ),
+        ],
       ),
     ];
   }

packages/moxxmpp/test/xeps/xep_0386_test.dart

@@ -78,4 +78,77 @@ void main() {
     expect(result.isType<NegotiatorError>(), false);
     expect(conn.resource, 'random.resource');
   });
+
+  test('Test simple Bind2 negotiation with a provided tag', () async {
+    final fakeSocket = StubTCPSocket([
+      StringExpectation(
+        "<stream:stream xmlns='jabber:client' version='1.0' xmlns:stream='http://etherx.jabber.org/streams' to='test.server' xml:lang='en'>",
+        '''
+<stream:stream
+    xmlns="jabber:client"
+    version="1.0"
+    xmlns:stream="http://etherx.jabber.org/streams"
+    from="test.server"
+    xml:lang="en">
+  <stream:features xmlns="http://etherx.jabber.org/streams">
+    <mechanisms xmlns="urn:ietf:params:xml:ns:xmpp-sasl">
+      <mechanism>PLAIN</mechanism>
+    </mechanisms>
+    <authentication xmlns='urn:xmpp:sasl:2'>
+      <mechanism>PLAIN</mechanism>
+      <inline>
+        <bind xmlns="urn:xmpp:bind:0" />
+      </inline>
+    </authentication>
+    <bind xmlns="urn:ietf:params:xml:ns:xmpp-bind">
+      <required/>
+    </bind>
+  </stream:features>''',
+      ),
+      StanzaExpectation(
+        "<authenticate xmlns='urn:xmpp:sasl:2' mechanism='PLAIN'><user-agent id='d4565fa7-4d72-4749-b3d3-740edbf87770'><software>moxxmpp</software><device>PapaTutuWawa's awesome device</device></user-agent><initial-response>AHBvbHlub21kaXZpc2lvbgBhYWFh</initial-response><bind xmlns='urn:xmpp:bind:0'><tag>moxxmpp</tag></bind></authenticate>",
+        '''
+<success xmlns='urn:xmpp:sasl:2'>
+  <authorization-identifier>polynomdivision@test.server/moxxmpp.random.resource</authorization-identifier>
+</success>
+        ''',
+      ),
+    ]);
+    final conn = XmppConnection(
+      TestingReconnectionPolicy(),
+      AlwaysConnectedConnectivityManager(),
+      fakeSocket,
+    )..setConnectionSettings(
+        ConnectionSettings(
+          jid: JID.fromString('polynomdivision@test.server'),
+          password: 'aaaa',
+          useDirectTLS: true,
+        ),
+      );
+    await conn.registerManagers([
+      RosterManager(TestingRosterStateManager('', [])),
+      DiscoManager([]),
+    ]);
+    await conn.registerFeatureNegotiators([
+      SaslPlainNegotiator(),
+      ResourceBindingNegotiator(),
+      Bind2Negotiator()
+        ..tag = 'moxxmpp',
+      Sasl2Negotiator(
+        userAgent: const UserAgent(
+          id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
+          software: 'moxxmpp',
+          device: "PapaTutuWawa's awesome device",
+        ),
+      ),
+    ]);
+
+    final result = await conn.connect(
+      waitUntilLogin: true,
+      shouldReconnect: false,
+      enableReconnectOnSuccess: false,
+    );
+    expect(result.isType<NegotiatorError>(), false);
+    expect(conn.resource, 'moxxmpp.random.resource');
+  });
 }