Add auth handler to public API to enable mqtt5 enhanced authn

lib/client.js

@@ -438,6 +438,10 @@ MqttClient.prototype._handlePacket = function (packet, done) {
       this._handleConnack(packet)
       done()
       break
+    case 'auth':
+      this._handleAuth(packet)
+      done()
+      break
     case 'pingresp':
       this._handlePingresp(packet)
       done()
@@ -1104,6 +1108,13 @@ MqttClient.prototype._sendPacket = function (packet, cb, cbStorePut) {
   cbStorePut = cbStorePut || nop
 
   if (!this.connected) {
+    // allow auth packets to be sent while authenticating with the broker (mqtt5 enhanced auth)
+    if (packet.cmd === 'auth') {
+      this._shiftPingInterval()
+      sendPacket(this, packet, cb)
+      return
+    }
+
     debug('_sendPacket :: client not connected. Storing packet offline.')
     this._storePacket(packet, cb, cbStorePut)
     return
@@ -1263,6 +1274,45 @@ MqttClient.prototype._handleConnack = function (packet) {
   }
 }
 
+MqttClient.prototype._handleAuth = function (packet) {
+  var options = this.options
+  var version = options.protocolVersion
+  var rc = version === 5 ? packet.reasonCode : packet.returnCode
+
+  if (version !== 5) {
+    var err = new Error('Protocol error: Auth packets are only supported in MQTT 5. Your version:' + version)
+    err.code = rc
+    this.emit('error', err)
+    return
+  }
+
+  var that = this
+  this.handleAuth(packet, function (err, packet) {
+    if (err) {
+      that.emit('error', err)
+      return
+    }
+
+    if (rc === 24) {
+      that.reconnecting = false
+      that._sendPacket(packet)
+    } else {
+      var error = new Error('Connection refused: ' + errors[rc])
+      err.code = rc
+      that.emit('error', error)
+    }
+  })
+}
+
+/**
+ * @param packet the packet received by the broker
+ * @return the auth packet to be returned to the broker
+ * @api public
+ */
+MqttClient.prototype.handleAuth = function (packet, callback) {
+  callback()
+}
+
 /**
  * _handlePublish
  *

types/lib/client.d.ts

@@ -8,7 +8,7 @@ import {
   IClientReconnectOptions
 } from './client-options'
 import { Store } from './store'
-import { Packet, IConnectPacket, IPublishPacket, IDisconnectPacket, QoS } from 'mqtt-packet'
+import { IAuthPacket, IConnectPacket, IPublishPacket, IDisconnectPacket, Packet, QoS } from 'mqtt-packet'
 
 export interface ISubscriptionGrant {
   /**
@@ -232,6 +232,15 @@ export declare class MqttClient extends events.EventEmitter {
    */
   public handleMessage (packet: Packet, callback: PacketCallback): void
 
+  /**
+   * Handler to handle auth packages to implement mqtt5 enhanced auth procedures
+   *
+   * @param packet the auth packet to handle
+   * @param callback call when finished
+   * @api public
+   */
+  public handleAuth (packet: IAuthPacket, callback: PacketCallback): void
+
   /**
    * getLastMessageId
    */