NotSupportedException: Extended authentication handler is not yet supported

[BEagle1984]

Describe the bug

While connecting to emqx we often get the "Extended authentication handler is not yet supported" exception. My library automatically retries after 500ms and it eventually successfully connects. Of course, no setting is being changed in between the retries.

Which component is your bug related to?

• Client

To Reproduce

Steps to reproduce the behavior:

1. Using MQTTnet 4.2.1.781
2. Try to connect to EMQX from a couple of pods running on AWS EKS.
3. The first try often fails with a NotSupportedException (Extended authentication handler is not yet supported)

Expected behavior

The connection always succeeds.

Additional context / logging

This is the exception we get:

MQTTnet.Adapter.MqttConnectingFailedException: Error while authenticating. Extended authentication handler is not yet supported
 ---> System.NotSupportedException: Extended authentication handler is not yet supported
   at MQTTnet.Client.MqttClient.Authenticate(IMqttChannelAdapter channelAdapter, MqttClientOptions options, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at MQTTnet.Client.MqttClient.Authenticate(IMqttChannelAdapter channelAdapter, MqttClientOptions options, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.ConnectInternal(IMqttChannelAdapter channelAdapter, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.ConnectAsync(MqttClientOptions options, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.ConnectAsync(MqttClientOptions options, CancellationToken cancellationToken)
   at Silverback.Messaging.Broker.Mqtt.MqttClientWrapper.TryConnectClientAsync(Boolean isFirstTry, CancellationToken cancellationToken)

It's not thrown for all clients instantiated within the same application and not always for the same ones.

Code example

The actual code uses Silverback, which wraps MQTTnet. The resulting MQTTnet related code is something like this:

IMqttClient mqttClient = MqttFactory.CreateClient();
await mqttClient.ConnectAsync(options, cancellationToken);

The options passed look like this:

  {MQTTnet.Client.MqttClientOptions}
    AllowPacketFragmentation: true
    AuthenticationData: null
    AuthenticationMethod: null
    ChannelOptions: {mqtt:1883}
    CleanSession: true
    ClientId: "Xyz_Xyz_9a3c0f23-70e7-43f2-b266-907fafb19371"
    Credentials: {MQTTnet.Client.MqttClientCredentials}
    ExtendedAuthenticationExchangeHandler: null
    KeepAlivePeriod: {00:00:15}
    MaximumPacketSize: 0
    ProtocolVersion: V500
    ReceiveMaximum: 0
    RequestProblemInformation: true
    RequestResponseInformation: false
    SessionExpiryInterval: 0
    ThrowOnNonSuccessfulConnectResponse: true
    Timeout: {00:01:40}
    TopicAliasMaximum: 0
    TryPrivate: true
    UserProperties: {Count = 0}
    ValidateFeatures: true
    WillContentType: null
    WillCorrelationData: null
    WillDelayInterval: 0
    WillMessageExpiryInterval: 0
    WillPayload: null
    WillPayloadFormatIndicator: Unspecified
    WillQualityOfServiceLevel: AtMostOnce
    WillResponseTopic: null
    WillRetain: false
    WillTopic: null
    WillUserProperties: {Count = 0}
    WriterBufferSize: 4096
    WriterBufferSizeMax: 65535

The guid in the ClientId is the Kubernetes pod id.

[BillArmstrong]

This is related to issue #2095. That issue is closed and resolved with pull request #2132. This issue possibly can be closed as enhanced authentication (previously called extended authentication in the v4 library) is now properly supported as of the v5 release.