fix(xep): When using FAST, fallback to other SASL mechanisms on failure

packages/moxxmpp/lib/src/negotiators/sasl2.dart

@@ -53,10 +53,15 @@ abstract class Sasl2AuthenticationNegotiator extends SaslNegotiator
   /// the base64-encoded response data.
   Future<String> getRawStep(String input);
 
+  /// Tells the negotiator that it has been selected as the SASL negotiator for SASL2.
   void pickForSasl2() {
     _pickedForSasl2 = true;
   }
 
+  /// When SASL2 fails, should we retry (true) or just fail (false).
+  /// Defaults to just returning false.
+  bool shouldRetrySasl() => false;
+
   @override
   void reset() {
     _pickedForSasl2 = false;
@@ -289,6 +294,16 @@ class Sasl2Negotiator extends XmppFeatureNegotiatorBase {
             await negotiator.onSasl2Failure(nonza);
           }
 
+          // Check if we should retry and, if we should, reset the current
+          // negotiator, this negotiator, and retry.
+          if (_currentSaslNegotiator!.shouldRetrySasl()) {
+            _currentSaslNegotiator!.reset();
+            reset();
+            return const Result(
+              NegotiatorState.retryLater,
+            );
+          }
+
           return Result(
             SaslError.fromFailure(nonza),
           );

packages/moxxmpp/lib/src/xeps/staging/fast.dart

@@ -30,10 +30,14 @@ class FASTToken {
   );
 
   factory FASTToken.fromXml(XMLNode token) {
-    assert(token.tag == 'token',
+    assert(
-        'Token can only be deserialised from a <token /> element',);
+      token.tag == 'token',
-    assert(token.xmlns == fastXmlns,
+      'Token can only be deserialised from a <token /> element',
-        'Token can only be deserialised from a <token /> element',);
+    );
+    assert(
+      token.xmlns == fastXmlns,
+      'Token can only be deserialised from a <token /> element',
+    );
 
     return FASTToken(
       token.attributes['token']! as String,
@@ -80,7 +84,8 @@ class FASTSaslNegotiator extends Sasl2AuthenticationNegotiator {
   @override
   bool canInlineFeature(List<XMLNode> features) {
     return features.firstWhereOrNull(
-            (child) => child.tag == 'fast' && child.xmlns == fastXmlns,) !=
+          (child) => child.tag == 'fast' && child.xmlns == fastXmlns,
+        ) !=
         null;
   }
 
@@ -114,6 +119,9 @@ class FASTSaslNegotiator extends Sasl2AuthenticationNegotiator {
     );
   }
 
+  @override
+  bool shouldRetrySasl() => true;
+
   @override
   Future<List<XMLNode>> onSasl2FeaturesReceived(XMLNode sasl2Features) async {
     if (fastToken != null && pickedForSasl2) {

packages/moxxmpp/test/xeps/xep_xxxx_fast_test.dart

@@ -160,4 +160,110 @@ void main() {
     expect(conn.resource, 'MU29eEZn');
     expect(fakeSocket.getState(), 7);
   });
+
+  test('Test failed FAST authentication with a token', () 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>
+      <mechanism>HT-SHA-256-NONE</mechanism>
+    </mechanisms>
+    <authentication xmlns='urn:xmpp:sasl:2'>
+      <mechanism>PLAIN</mechanism>
+      <mechanism>HT-SHA-256-NONE</mechanism>
+      <mechanism>HT-SHA-256-ENDP</mechanism>
+      <inline>
+        <bind xmlns="urn:xmpp:bind:0" />
+        <fast xmlns="urn:xmpp:fast:0">
+          <mechanism>HT-SHA-256-NONE</mechanism>
+          <mechanism>HT-SHA-256-ENDP</mechanism>
+        </fast>
+      </inline>
+    </authentication>
+    <bind xmlns="urn:ietf:params:xml:ns:xmpp-bind">
+      <required/>
+    </bind>
+  </stream:features>''',
+      ),
+      StanzaExpectation(
+        "<authenticate xmlns='urn:xmpp:sasl:2' mechanism='HT-SHA-256-NONE'><user-agent id='d4565fa7-4d72-4749-b3d3-740edbf87770'><software>moxxmpp</software><device>PapaTutuWawa's awesome device</device></user-agent><initial-response>WXZzciBwYmFmdmZnZiBqdmd1IGp2eXFhcmZm</initial-response><fast xmlns='urn:xmpp:fast:0' /></authenticate>",
+        '''
+<failure xmlns='urn:xmpp:sasl:2'>
+  <not-authorized xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
+</failure>
+        ''',
+      ),
+      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><request-token xmlns='urn:xmpp:fast:0' mechanism='HT-SHA-256-NONE' /></authenticate>",
+        '''
+<success xmlns='urn:xmpp:sasl:2'>
+  <authorization-identifier>polynomdivision@test.server</authorization-identifier>
+  <token xmlns='urn:xmpp:fast:0' 
+           expiry='2020-03-12T14:36:15Z' 
+           token='ed00e36cb42449a365a306a413f51ffd5ea8' />
+</success>
+        ''',
+      ),
+      StanzaExpectation(
+        '<iq xmlns="jabber:client" type="set" id="a"><bind xmlns="urn:ietf:params:xml:ns:xmpp-bind"/></iq>',
+        '<iq xmlns="jabber:client" type="result" id="a"><bind xmlns="urn:ietf:params:xml:ns:xmpp-bind"><jid>polynomdivision@test.server/MU29eEZn</jid></bind></iq>',
+        ignoreId: true,
+      ),
+    ]);
+    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(),
+      FASTSaslNegotiator()
+        ..fastToken = const FASTToken(
+          'WXZzciBwYmFmdmZnZiBqdmd1IGp2eXFhcmZm',
+          '2020-03-12T14:36:15Z',
+        ),
+      Sasl2Negotiator(
+        userAgent: const UserAgent(
+          id: 'd4565fa7-4d72-4749-b3d3-740edbf87770',
+          software: 'moxxmpp',
+          device: "PapaTutuWawa's awesome device",
+        ),
+      ),
+    ]);
+
+    final result1 = await conn.connect(
+      waitUntilLogin: true,
+      shouldReconnect: false,
+      enableReconnectOnSuccess: false,
+    );
+    expect(result1.isType<NegotiatorError>(), false);
+    expect(conn.resource, 'MU29eEZn');
+    expect(fakeSocket.getState(), 4);
+
+    final token = conn
+        .getNegotiatorById<FASTSaslNegotiator>(saslFASTNegotiator)!
+        .fastToken;
+    expect(token != null, true);
+    expect(token!.token, 'ed00e36cb42449a365a306a413f51ffd5ea8');
+  });
 }