diff --git a/ChangeLog.txt b/ChangeLog.txt
index b214eb2b..11e35caa 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -170,6 +170,9 @@ Client library:
   gives access to reason codes for each of the unsubscription requests.
 - Add `mosquitto_property_remove`, for removing properties from property
   lists.
+- Add `on_ext_auth()` callback to allow handling MQTT v5 extended authentication.
+- Add `mosquitto_ext_auth_continue()` function to continue an MQTT v5 extended
+  authentication.
 
 Clients:
 - Add `-W` timeout support to Windows.
diff --git a/include/mosquitto/libmosquitto_auth.h b/include/mosquitto/libmosquitto_auth.h
index 30480596..a9df5454 100644
--- a/include/mosquitto/libmosquitto_auth.h
+++ b/include/mosquitto/libmosquitto_auth.h
@@ -56,6 +56,26 @@ extern "C" {
  */
 libmosq_EXPORT int mosquitto_username_pw_set(struct mosquitto *mosq, const char *username, const char *password);
 
+/*
+ * Function: mosquitto_ext_auth_continue
+ *
+ * Use within an on_ext_auth callback only.
+ *
+ * Call to continue the MQTT v5 extended authentication flow.
+ *
+ * Parameters:
+ * 	mosq -          a valid mosquitto instance.
+ * 	auth_method -   the authentication method as provided in the on_ext_auth callback
+ * 	auth_data -     authentication data to send to the broker, or NULL
+ * 	auth_data_len - the length of auth_data, in bytes, or 0
+ *
+ * Returns:
+ * 	MOSQ_ERR_SUCCESS - on success.
+ * 	MOSQ_ERR_INVAL -   if the input parameters were invalid.
+ * 	MOSQ_ERR_NOMEM -   if an out of memory condition occurred.
+ */
+libmosq_EXPORT int mosquitto_ext_auth_continue(struct mosquitto *context, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/include/mosquitto/libmosquitto_callbacks.h b/include/mosquitto/libmosquitto_callbacks.h
index c522e00d..b560ee45 100644
--- a/include/mosquitto/libmosquitto_callbacks.h
+++ b/include/mosquitto/libmosquitto_callbacks.h
@@ -410,6 +410,38 @@ libmosq_EXPORT void mosquitto_unsubscribe_v5_callback_set(struct mosquitto *mosq
  */
 libmosq_EXPORT void mosquitto_unsubscribe2_v5_callback_set(struct mosquitto *mosq, void (*on_unsubscribe)(struct mosquitto *, void *, int, int, const int *, const mosquitto_property *props));
 
+/*
+ * Function: mosquitto_ext_auth_callback_set
+ *
+ * Set the callback for extended authentication. This should be used if you
+ * want to support MQTT v5.0 extended authentication.
+ *
+ *  mosq -        a valid mosquitto instance.
+ *  on_ext_auth - a callback function in the following form:
+ *                void callback(struct mosquitto *mosq, void *obj, const char *auth_method, int auth_data_len, const void *auth_data, const mosquitto_property *props)
+ *
+ * Callback Parameters:
+ *  mosq -          the mosquitto instance making the callback.
+ *  obj -           the user data provided in <mosquitto_new>
+ *  auth_method -   the authentication method provided by the broker
+ *  auth_data_len - the length of auth_data in bytes
+ *  auth_data -     the authentication data, or NULL
+ *  props -         list of MQTT 5 properties sent
+ *                  note that this includes the auth-method and auth-data
+ *                  properties, so you cannot use it directly with
+ *                  mosquitto_ext_auth_continue and must instead create your
+ *                  own property list
+ *
+ * Callback Return:
+ *  MOSQ_ERR_SUCCESS - if you accept the authentication data
+ *  MOSQ_ERR_AUTH    - if the authentication should fail
+ *  MOSQ_ERR_NOMEM   - on out of memory
+ *
+ * See Also:
+ *    <mosquitto_ext_auth_continue>
+ */
+void mosquitto_ext_auth_callback_set(struct mosquitto *mosq, int (*on_auth)(struct mosquitto *, void *, const char *, uint16_t, const void *, const mosquitto_property *props));
+
 /*
  * Function: mosquitto_log_callback_set
  *
diff --git a/include/mosquitto/libmosquittopp.h b/include/mosquitto/libmosquittopp.h
index 4d99e240..3226526e 100644
--- a/include/mosquitto/libmosquittopp.h
+++ b/include/mosquitto/libmosquittopp.h
@@ -120,6 +120,7 @@ class mosqpp_EXPORT mosquittopp {
 		void message_retry_set(unsigned int message_retry);
 		void user_data_set(void *userdata);
 		int tls_set(const char *cafile, const char *capath=NULL, const char *certfile=NULL, const char *keyfile=NULL, int (*pw_callback)(char *buf, int size, int rwflag, void *userdata)=NULL);
+		int ext_auth_continue(const char *auth_method, uint16_t auth_data_len=0, const void *auth_data=NULL, const mosquitto_property *properties=NULL);
 		int tls_opts_set(int cert_reqs, const char *tls_version=NULL, const char *ciphers=NULL);
 		int tls_insecure_set(bool value);
 		int tls_psk_set(const char *psk, const char *identity, const char *ciphers=NULL);
@@ -156,6 +157,7 @@ class mosqpp_EXPORT mosquittopp {
 		virtual void on_unsubscribe_v5(int /*mid*/, const mosquitto_property * /*props*/) {return;}
 		virtual void on_log(int /*level*/, const char * /*str*/) {return;}
 		virtual void on_error() {return;}
+		virtual int on_ext_auth(const char * /*auth_method*/, uint16_t /*auth_data_len*/, const void * /*auth_data*/, const mosquitto_property * /*props*/) {return MOSQ_ERR_AUTH;}
 };
 
 }
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 187b9498..4db1074a 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -10,6 +10,7 @@ set(C_SRC
 	alias_mosq.c alias_mosq.h
 	callbacks.c
 	connect.c
+	extended_auth.c
 	handle_auth.c
 	handle_connack.c
 	handle_disconnect.c
diff --git a/lib/Makefile b/lib/Makefile
index d7ef9b93..602a5955 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -46,6 +46,7 @@ OBJS= \
 	alias_mosq.o \
 	callbacks.o \
 	connect.o \
+	extended_auth.o \
 	handle_auth.o \
 	handle_connack.o \
 	handle_disconnect.o \
diff --git a/lib/callbacks.c b/lib/callbacks.c
index 5e7490ba..a8eff182 100644
--- a/lib/callbacks.c
+++ b/lib/callbacks.c
@@ -136,6 +136,14 @@ void mosquitto_log_callback_set(struct mosquitto *mosq, void (*on_log)(struct mo
 }
 
 
+void mosquitto_ext_auth_callback_set(struct mosquitto *mosq, int (*on_ext_auth)(struct mosquitto *, void *, const char *, uint16_t, const void *, const mosquitto_property *props))
+{
+	pthread_mutex_lock(&mosq->callback_mutex);
+	mosq->on_ext_auth = on_ext_auth;
+	pthread_mutex_unlock(&mosq->callback_mutex);
+}
+
+
 void callback__on_pre_connect(struct mosquitto *mosq)
 {
 	void (*on_pre_connect)(struct mosquitto *, void *userdata);
@@ -286,3 +294,20 @@ void callback__on_disconnect(struct mosquitto *mosq, int rc, const mosquitto_pro
 	}
 	mosq->callback_depth--;
 }
+
+int callback__on_ext_auth(struct mosquitto *mosq, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *properties)
+{
+	int rc = MOSQ_ERR_AUTH;
+	int (*on_ext_auth)(struct mosquitto *, void *userdata, const char *, uint16_t, const void *, const mosquitto_property *props);
+
+	pthread_mutex_lock(&mosq->callback_mutex);
+	on_ext_auth = mosq->on_ext_auth;
+	pthread_mutex_unlock(&mosq->callback_mutex);
+
+	mosq->callback_depth++;
+	if(on_ext_auth){
+		rc = on_ext_auth(mosq, mosq->userdata, auth_method, auth_data_len, auth_data, properties);
+	}
+	mosq->callback_depth--;
+	return rc;
+}
diff --git a/lib/callbacks.h b/lib/callbacks.h
index fb33d547..8acc21ea 100644
--- a/lib/callbacks.h
+++ b/lib/callbacks.h
@@ -27,5 +27,6 @@ void callback__on_message(struct mosquitto *mosq, const struct mosquitto_message
 void callback__on_subscribe(struct mosquitto *mosq, int mid, int qos_count, const int *granted_qos, const mosquitto_property *props);
 void callback__on_unsubscribe(struct mosquitto *mosq, int mid, int reason_code_count, const int *reason_codes, const mosquitto_property *props);
 void callback__on_disconnect(struct mosquitto *mosq, int rc, const mosquitto_property *props);
+int callback__on_ext_auth(struct mosquitto *mosq, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *properties);
 
 #endif
diff --git a/lib/cpp/mosquittopp.cpp b/lib/cpp/mosquittopp.cpp
index 2d3b5d86..683e88ca 100644
--- a/lib/cpp/mosquittopp.cpp
+++ b/lib/cpp/mosquittopp.cpp
@@ -125,6 +125,14 @@ static void on_unsubscribe_v5_wrapper(struct mosquitto *mosq, void *userdata, in
 }
 
 
+static int on_ext_auth_wrapper(struct mosquitto *mosq, void *userdata, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props)
+{
+	class mosquittopp *m = (class mosquittopp *)userdata;
+	UNUSED(mosq);
+	return m->on_ext_auth(auth_method, auth_data_len, auth_data, props);
+}
+
+
 static void on_log_wrapper(struct mosquitto *mosq, void *userdata, int level, const char *str)
 {
 	class mosquittopp *m = (class mosquittopp *)userdata;
@@ -273,6 +281,7 @@ void mosquitto_callbacks_set(struct mosquitto *mosq) {
 	mosquitto_subscribe_v5_callback_set(mosq, on_subscribe_v5_wrapper);
 	mosquitto_unsubscribe_callback_set(mosq, on_unsubscribe_wrapper);
 	mosquitto_unsubscribe_v5_callback_set(mosq, on_unsubscribe_v5_wrapper);
+	mosquitto_ext_auth_callback_set(mosq, on_ext_auth_wrapper);
 	mosquitto_log_callback_set(mosq, on_log_wrapper);
 }
 }
@@ -345,6 +354,11 @@ int mosquittopp::disconnect_v5(int reason_code, const mosquitto_property *proper
 	return mosquitto_disconnect_v5(m_mosq, reason_code, properties);
 }
 
+int mosquittopp::ext_auth_continue(const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *properties)
+{
+	return mosquitto_ext_auth_continue(m_mosq, auth_method, auth_data_len, auth_data, properties);
+}
+
 int mosquittopp::socket()
 {
 	return mosquitto_socket(m_mosq);
diff --git a/lib/extended_auth.c b/lib/extended_auth.c
new file mode 100644
index 00000000..949ef5b0
--- /dev/null
+++ b/lib/extended_auth.c
@@ -0,0 +1,64 @@
+/*
+Copyright (c) 2019-2024 Roger Light <roger@atchoo.org>
+
+All rights reserved. This program and the accompanying materials
+are made available under the terms of the Eclipse Public License 2.0
+and Eclipse Distribution License v1.0 which accompany this distribution.
+
+The Eclipse Public License is available at
+   https://www.eclipse.org/legal/epl-2.0/
+and the Eclipse Distribution License is available at
+  http://www.eclipse.org/org/documents/edl-v10.php.
+
+SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
+
+Contributors:
+   Roger Light - initial implementation and documentation.
+*/
+
+#include "config.h"
+
+#include "mosquitto/mqtt_protocol.h"
+#include "packet_mosq.h"
+#include "property_mosq.h"
+#include "util_mosq.h"
+
+int mosquitto_ext_auth_continue(struct mosquitto *context, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *input_props)
+{
+	struct mosquitto__packet *packet = NULL;
+	int rc;
+	uint32_t remaining_length;
+	mosquitto_property *properties = NULL;
+
+	rc = mosquitto_property_copy_all(&properties, input_props);
+	if(rc) return rc;
+
+	if(!context || context->protocol != mosq_p_mqtt5 || !auth_method) return MOSQ_ERR_PROTOCOL;
+
+	remaining_length = 1;
+
+	rc = mosquitto_property_add_string(&properties, MQTT_PROP_AUTHENTICATION_METHOD, auth_method);
+	if(rc) goto error;
+
+	if(auth_data != NULL && auth_data_len > 0){
+		rc = mosquitto_property_add_binary(&properties, MQTT_PROP_AUTHENTICATION_DATA, auth_data, auth_data_len);
+		if(rc) goto error;
+	}
+
+	remaining_length += mosquitto_property_get_remaining_length(properties);
+
+	rc = packet__check_oversize(context, remaining_length);
+	if(rc) goto error;
+
+	rc = packet__alloc(&packet, CMD_AUTH, remaining_length);
+	if(rc) goto error;
+
+	packet__write_byte(packet, MQTT_RC_CONTINUE_AUTHENTICATION);
+	property__write_all(packet, properties, true);
+	mosquitto_property_free_all(&properties);
+
+	return packet__queue(context, packet);
+error:
+	mosquitto_property_free_all(&properties);
+	return rc;
+}
diff --git a/lib/handle_auth.c b/lib/handle_auth.c
index 5907e483..796289cc 100644
--- a/lib/handle_auth.c
+++ b/lib/handle_auth.c
@@ -21,6 +21,7 @@ Contributors:
 #include <stdio.h>
 #include <string.h>
 
+#include "callbacks.h"
 #include "logging_mosq.h"
 #include "mosquitto_internal.h"
 #include "mosquitto/mqtt_protocol.h"
@@ -33,6 +34,9 @@ int handle__auth(struct mosquitto *mosq)
 {
 	int rc = 0;
 	uint8_t reason_code;
+	char *auth_method = NULL;
+	void *auth_data = NULL;
+	uint16_t auth_data_len = 0;
 	mosquitto_property *properties = NULL;
 
 	if(!mosq) return MOSQ_ERR_INVAL;
@@ -49,7 +53,11 @@ int handle__auth(struct mosquitto *mosq)
 
 	rc = property__read_all(CMD_AUTH, &mosq->in_packet, &properties);
 	if(rc) return rc;
-	mosquitto_property_free_all(&properties); /* FIXME - TEMPORARY UNTIL PROPERTIES PROCESSED */
 
-	return MOSQ_ERR_SUCCESS;
+	mosquitto_property_read_string(properties, MQTT_PROP_AUTHENTICATION_METHOD, &auth_method, false);
+	mosquitto_property_read_binary(properties, MQTT_PROP_AUTHENTICATION_DATA, &auth_data, &auth_data_len, false);
+	rc = callback__on_ext_auth(mosq, auth_method, auth_data_len, auth_data, properties);
+	mosquitto_property_free_all(&properties);
+
+	return rc;
 }
diff --git a/lib/linker.version b/lib/linker.version
index b1313f6d..7f8dbd0a 100644
--- a/lib/linker.version
+++ b/lib/linker.version
@@ -144,6 +144,8 @@ MOSQ_1.7 {
 
 MOSQ_2.1 {
 	global:
+		mosquitto_ext_auth_callback_set;
+		mosquitto_ext_auth_continue;
 		mosquitto_pre_connect_callback_set;
 		mosquitto_topic_matches_sub_with_pattern;
 		mosquitto_sub_matches_acl;
diff --git a/lib/mosquitto_internal.h b/lib/mosquitto_internal.h
index b48c00d2..f4fd487f 100644
--- a/lib/mosquitto_internal.h
+++ b/lib/mosquitto_internal.h
@@ -405,6 +405,7 @@ struct mosquitto {
 	void (*on_unsubscribe)(struct mosquitto *, void *userdata, int mid);
 	void (*on_unsubscribe_v5)(struct mosquitto *, void *userdata, int mid, const mosquitto_property *props);
 	void (*on_unsubscribe2_v5)(struct mosquitto *, void *userdata, int mid, int reason_code_count, const int *reason_codes, const mosquitto_property *props);
+	int (*on_ext_auth)(struct mosquitto *, void *userdata, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props);
 	void (*on_log)(struct mosquitto *, void *userdata, int level, const char *str);
 	/*void (*on_error)();*/
 	char *host;
diff --git a/test/lib/01-extended-auth-continue.py b/test/lib/01-extended-auth-continue.py
new file mode 100755
index 00000000..bccbe799
--- /dev/null
+++ b/test/lib/01-extended-auth-continue.py
@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+
+from mosq_test_helper import *
+import mqtt5_rc
+
+def do_test(conn, data):
+    props = mqtt5_props.gen_uint32_prop(mqtt5_props.PROP_MAXIMUM_PACKET_SIZE, 1000)
+    props += mqtt5_props.gen_uint16_prop(mqtt5_props.PROP_RECEIVE_MAXIMUM, 20)
+    connect_packet = mosq_test.gen_connect("01-extended-auth", proto_ver=5, properties=props)
+
+    props = mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_METHOD, "test-method")
+    props += mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_DATA, "test-request") # This is really a binary property
+    auth_continue_b2c = mosq_test.gen_auth(reason_code=mqtt5_rc.MQTT_RC_CONTINUE_AUTHENTICATION, properties=props)
+
+    props = mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_METHOD, "test-method")
+    props += mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_DATA, "test-reply") # This is really a binary property
+    auth_continue_c2b = mosq_test.gen_auth(reason_code=mqtt5_rc.MQTT_RC_CONTINUE_AUTHENTICATION, properties=props)
+    connack_packet = mosq_test.gen_connack(rc=0, proto_ver=5)
+
+    disconnect_packet = mosq_test.gen_disconnect(proto_ver=5)
+
+    mosq_test.do_receive_send(conn, connect_packet, auth_continue_b2c, "auth_b2c")
+    mosq_test.do_receive_send(conn, auth_continue_c2b, connack_packet, "connack")
+    mosq_test.expect_packet(conn, "disconnect", disconnect_packet)
+
+
+mosq_test.client_test("c/01-extended-auth-continue.test", [], do_test, None)
+mosq_test.client_test("cpp/01-extended-auth-continue.test", [], do_test, None)
diff --git a/test/lib/01-extended-auth-failure.py b/test/lib/01-extended-auth-failure.py
new file mode 100755
index 00000000..1e04ef68
--- /dev/null
+++ b/test/lib/01-extended-auth-failure.py
@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+
+from mosq_test_helper import *
+import mqtt5_rc
+
+def do_test(conn, data):
+    props = mqtt5_props.gen_uint32_prop(mqtt5_props.PROP_MAXIMUM_PACKET_SIZE, 1000)
+    props += mqtt5_props.gen_uint16_prop(mqtt5_props.PROP_RECEIVE_MAXIMUM, 20)
+    connect_packet = mosq_test.gen_connect("01-extended-auth", proto_ver=5, properties=props)
+
+    props = mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_METHOD, "test-method")
+    props += mqtt5_props.gen_string_prop(mqtt5_props.PROP_AUTHENTICATION_DATA, "test-request") # This is really a binary property
+    auth_continue_b2c = mosq_test.gen_auth(reason_code=mqtt5_rc.MQTT_RC_CONTINUE_AUTHENTICATION, properties=props)
+
+    disconnect_packet = mosq_test.gen_disconnect(proto_ver=5)
+
+    mosq_test.do_receive_send(conn, connect_packet, auth_continue_b2c, "auth_b2c")
+    p = conn.recv(1)
+    if len(p) == 1:
+        exit(1)
+
+
+mosq_test.client_test("c/01-extended-auth-failure.test", [], do_test, None)
+mosq_test.client_test("cpp/01-extended-auth-failure.test", [], do_test, None)
diff --git a/test/lib/Makefile b/test/lib/Makefile
index 5f010bda..9016d2a2 100644
--- a/test/lib/Makefile
+++ b/test/lib/Makefile
@@ -30,6 +30,8 @@ test : test-compile
 	./01-con-discon-will.py
 	./01-con-discon-will-v5.py
 	./01-con-discon-will-clear.py
+	./01-extended-auth-continue.py
+	./01-extended-auth-failure.py
 	./01-keepalive-pingreq.py
 	./01-no-clean-session.py
 	./01-server-keepalive-pingreq.py
diff --git a/test/lib/c/01-extended-auth-continue.c b/test/lib/c/01-extended-auth-continue.c
new file mode 100644
index 00000000..d808c266
--- /dev/null
+++ b/test/lib/c/01-extended-auth-continue.c
@@ -0,0 +1,89 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <mosquitto.h>
+#include <mosquitto/mqtt_protocol.h>
+
+static int run = -1;
+
+static void on_connect(struct mosquitto *mosq, void *obj, int rc, int flags, const mosquitto_property *properties)
+{
+	(void)obj;
+	(void)rc;
+	(void)flags;
+	(void)properties;
+
+	/* FIXME - should verify flags and all properties here. */
+	if(rc){
+		exit(1);
+	}else{
+		mosquitto_disconnect(mosq);
+	}
+}
+
+static int on_ext_auth(struct mosquitto *mosq, void *obj, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *properties)
+{
+	(void)obj;
+	(void)auth_data;
+	(void)auth_data_len;
+	(void)properties;
+
+	if(strcmp(auth_method, "test-method")){
+		run = 1;
+		return MOSQ_ERR_AUTH;
+	}
+	if(auth_data_len == 0 || (!auth_data || strcmp(auth_data, "test-request"))){
+		run = 1;
+		return MOSQ_ERR_AUTH;
+	}
+	return mosquitto_ext_auth_continue(mosq, auth_method, strlen("test-reply"), "test-reply", NULL);
+}
+
+static void on_disconnect(struct mosquitto *mosq, void *obj, int rc, const mosquitto_property *properties)
+{
+	(void)mosq;
+	(void)obj;
+	(void)properties;
+
+	/* FIXME - should verify flags and all properties here. */
+	run = rc;
+}
+
+int main(int argc, char *argv[])
+{
+	int rc;
+	struct mosquitto *mosq;
+	int port;
+	mosquitto_property *props = NULL;
+
+	if(argc < 2){
+		return 1;
+	}
+	port = atoi(argv[1]);
+
+	mosquitto_lib_init();
+
+	mosq = mosquitto_new("01-extended-auth", true, NULL);
+	if(mosq == NULL){
+		return 1;
+	}
+	mosquitto_int_option(mosq, MOSQ_OPT_PROTOCOL_VERSION, 5);
+	mosquitto_connect_v5_callback_set(mosq, on_connect);
+	mosquitto_ext_auth_callback_set(mosq, on_ext_auth);
+	mosquitto_disconnect_v5_callback_set(mosq, on_disconnect);
+
+	mosquitto_property_add_int32(&props, MQTT_PROP_MAXIMUM_PACKET_SIZE, 1000);
+	rc = mosquitto_connect_bind_v5(mosq, "localhost", port, 60, NULL, props);
+	mosquitto_property_free_all(&props);
+	if(rc != MOSQ_ERR_SUCCESS) return rc;
+
+	while(run == -1){
+		mosquitto_loop(mosq, -1, 1);
+	}
+
+	mosquitto_destroy(mosq);
+
+	mosquitto_lib_cleanup();
+	return run;
+}
diff --git a/test/lib/c/01-extended-auth-failure.c b/test/lib/c/01-extended-auth-failure.c
new file mode 100644
index 00000000..2db090c1
--- /dev/null
+++ b/test/lib/c/01-extended-auth-failure.c
@@ -0,0 +1,83 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <mosquitto.h>
+#include <mosquitto/mqtt_protocol.h>
+
+static int run = -1;
+
+static void on_connect(struct mosquitto *mosq, void *obj, int rc, int flags, const mosquitto_property *properties)
+{
+	(void)obj;
+	(void)rc;
+	(void)flags;
+	(void)properties;
+
+	/* FIXME - should verify flags and all properties here. */
+	if(rc){
+		exit(1);
+	}else{
+		mosquitto_disconnect(mosq);
+	}
+}
+
+static int on_ext_auth(struct mosquitto *mosq, void *obj, const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *properties)
+{
+	(void)mosq;
+	(void)obj;
+	(void)auth_method;
+	(void)auth_data;
+	(void)auth_data_len;
+	(void)properties;
+
+	return MOSQ_ERR_AUTH;
+}
+
+static void on_disconnect(struct mosquitto *mosq, void *obj, int rc, const mosquitto_property *properties)
+{
+	(void)mosq;
+	(void)obj;
+	(void)properties;
+
+	/* FIXME - should verify flags and all properties here. */
+	run = rc;
+}
+
+int main(int argc, char *argv[])
+{
+	int rc;
+	struct mosquitto *mosq;
+	int port;
+	mosquitto_property *props = NULL;
+
+	if(argc < 2){
+		return 1;
+	}
+	port = atoi(argv[1]);
+
+	mosquitto_lib_init();
+
+	mosq = mosquitto_new("01-extended-auth", true, NULL);
+	if(mosq == NULL){
+		return 1;
+	}
+	mosquitto_int_option(mosq, MOSQ_OPT_PROTOCOL_VERSION, 5);
+	mosquitto_connect_v5_callback_set(mosq, on_connect);
+	mosquitto_ext_auth_callback_set(mosq, on_ext_auth);
+	mosquitto_disconnect_v5_callback_set(mosq, on_disconnect);
+
+	mosquitto_property_add_int32(&props, MQTT_PROP_MAXIMUM_PACKET_SIZE, 1000);
+	rc = mosquitto_connect_bind_v5(mosq, "localhost", port, 60, NULL, props);
+	mosquitto_property_free_all(&props);
+	if(rc != MOSQ_ERR_SUCCESS) return rc;
+
+	while(run == -1){
+		mosquitto_loop(mosq, -1, 1);
+	}
+
+	mosquitto_destroy(mosq);
+
+	mosquitto_lib_cleanup();
+	return run;
+}
diff --git a/test/lib/c/CMakeLists.txt b/test/lib/c/CMakeLists.txt
index 4e60249c..7b8cdb0f 100644
--- a/test/lib/c/CMakeLists.txt
+++ b/test/lib/c/CMakeLists.txt
@@ -4,6 +4,8 @@ set(BINARIES
     01-con-discon-will
     01-con-discon-will-clear
     01-con-discon-will-v5
+	01-extended-auth-continue
+	01-extended-auth-failure
     01-keepalive-pingreq
     01-no-clean-session
     01-pre-connect-callback
diff --git a/test/lib/c/Makefile b/test/lib/c/Makefile
index 1483ac54..11349c15 100644
--- a/test/lib/c/Makefile
+++ b/test/lib/c/Makefile
@@ -13,6 +13,8 @@ SRC = \
 	01-con-discon-will.c \
 	01-con-discon-will-v5.c \
 	01-con-discon-will-clear.c \
+	01-extended-auth-continue.c \
+	01-extended-auth-failure.c \
 	01-keepalive-pingreq.c \
 	01-no-clean-session.c \
 	01-pre-connect-callback.c \
diff --git a/test/lib/cpp/01-extended-auth-continue.cpp b/test/lib/cpp/01-extended-auth-continue.cpp
new file mode 100644
index 00000000..aae0737f
--- /dev/null
+++ b/test/lib/cpp/01-extended-auth-continue.cpp
@@ -0,0 +1,84 @@
+#include <cassert>
+#include <cstring>
+#include <mosquitto/libmosquittopp.h>
+
+static int run = -1;
+
+class mosquittopp_test : public mosqpp::mosquittopp
+{
+	public:
+		mosquittopp_test(const char *id);
+
+		void on_connect_v5(int rc, int flags, const mosquitto_property *props);
+		void on_disconnect_v5(int rc, const mosquitto_property *props);
+		int on_ext_auth(const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props);
+};
+
+mosquittopp_test::mosquittopp_test(const char *id) : mosqpp::mosquittopp(id)
+{
+}
+
+void mosquittopp_test::on_connect_v5(int rc, int flags, const mosquitto_property *props)
+{
+	assert(flags == 0);
+	assert(props);
+	assert(mosqpp::property_check_all(CMD_CONNACK, props) == MOSQ_ERR_SUCCESS);
+
+	if(rc){
+		exit(1);
+	}else{
+		disconnect();
+	}
+}
+
+void mosquittopp_test::on_disconnect_v5(int rc, const mosquitto_property *props)
+{
+	assert(props == NULL);
+	run = rc;
+}
+
+
+int mosquittopp_test::on_ext_auth(const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props)
+{
+	assert(props != NULL);
+
+	if(strcmp(auth_method, "test-method")){
+		run = 1;
+		return MOSQ_ERR_AUTH;
+	}
+	if(auth_data_len == 0 || (!auth_data || strcmp((const char *)auth_data, "test-request"))){
+		run = 1;
+		return MOSQ_ERR_AUTH;
+	}
+	return ext_auth_continue(auth_method, strlen("test-reply"), "test-reply", NULL);
+}
+
+
+int main(int argc, char *argv[])
+{
+	mosquittopp_test *mosq;
+	mosquitto_property *props = NULL;
+	int rc;
+
+	assert(argc == 2);
+	int port = atoi(argv[1]);
+
+	mosqpp::lib_init();
+
+	mosq = new mosquittopp_test("01-extended-auth");
+	mosq->int_option(MOSQ_OPT_PROTOCOL_VERSION, 5);
+
+	mosquitto_property_add_int32(&props, MQTT_PROP_MAXIMUM_PACKET_SIZE, 1000);
+	rc = mosq->connect_v5("localhost", port, 60, NULL, props);
+	mosquitto_property_free_all(&props);
+	if(rc != MOSQ_ERR_SUCCESS) return rc;
+
+	while(run == -1){
+		mosq->loop();
+	}
+	delete mosq;
+
+	mosqpp::lib_cleanup();
+
+	return run;
+}
diff --git a/test/lib/cpp/01-extended-auth-failure.cpp b/test/lib/cpp/01-extended-auth-failure.cpp
new file mode 100644
index 00000000..1d2fcf3e
--- /dev/null
+++ b/test/lib/cpp/01-extended-auth-failure.cpp
@@ -0,0 +1,78 @@
+#include <cassert>
+#include <cstring>
+#include <mosquitto/libmosquittopp.h>
+
+static int run = -1;
+
+class mosquittopp_test : public mosqpp::mosquittopp
+{
+	public:
+		mosquittopp_test(const char *id);
+
+		void on_connect_v5(int rc, int flags, const mosquitto_property *props);
+		void on_disconnect_v5(int rc, const mosquitto_property *props);
+		int on_ext_auth(const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props);
+};
+
+mosquittopp_test::mosquittopp_test(const char *id) : mosqpp::mosquittopp(id)
+{
+}
+
+void mosquittopp_test::on_connect_v5(int rc, int flags, const mosquitto_property *props)
+{
+	assert(flags == 0);
+	assert(props);
+	assert(mosqpp::property_check_all(CMD_CONNACK, props) == MOSQ_ERR_SUCCESS);
+
+	if(rc){
+		exit(1);
+	}else{
+		disconnect();
+	}
+}
+
+void mosquittopp_test::on_disconnect_v5(int rc, const mosquitto_property *props)
+{
+	assert(props == NULL);
+	run = rc;
+}
+
+
+int mosquittopp_test::on_ext_auth(const char *auth_method, uint16_t auth_data_len, const void *auth_data, const mosquitto_property *props)
+{
+	(void)auth_method;
+	(void)auth_data_len;
+	(void)auth_data;
+	(void)props;
+	return MOSQ_ERR_AUTH;
+}
+
+
+int main(int argc, char *argv[])
+{
+	mosquittopp_test *mosq;
+	mosquitto_property *props = NULL;
+	int rc;
+
+	assert(argc == 2);
+	int port = atoi(argv[1]);
+
+	mosqpp::lib_init();
+
+	mosq = new mosquittopp_test("01-extended-auth");
+	mosq->int_option(MOSQ_OPT_PROTOCOL_VERSION, 5);
+
+	mosquitto_property_add_int32(&props, MQTT_PROP_MAXIMUM_PACKET_SIZE, 1000);
+	rc = mosq->connect_v5("localhost", port, 60, NULL, props);
+	mosquitto_property_free_all(&props);
+	if(rc != MOSQ_ERR_SUCCESS) return rc;
+
+	while(run == -1){
+		mosq->loop();
+	}
+	delete mosq;
+
+	mosqpp::lib_cleanup();
+
+	return run;
+}
diff --git a/test/lib/cpp/CMakeLists.txt b/test/lib/cpp/CMakeLists.txt
index cb819e82..e71ed7ef 100644
--- a/test/lib/cpp/CMakeLists.txt
+++ b/test/lib/cpp/CMakeLists.txt
@@ -4,6 +4,8 @@ set(BINARIES
     01-con-discon-will-clear
     01-con-discon-will
     01-con-discon-will-v5
+    01-extended-auth-continue
+    01-extended-auth-failure
     01-keepalive-pingreq
     01-no-clean-session
     01-pre-connect-callback
diff --git a/test/lib/cpp/Makefile b/test/lib/cpp/Makefile
index 7e8a2b73..29664c68 100644
--- a/test/lib/cpp/Makefile
+++ b/test/lib/cpp/Makefile
@@ -12,6 +12,8 @@ SRC = \
 	01-con-discon-will-clear.cpp \
 	01-con-discon-will-v5.cpp \
 	01-con-discon-will.cpp \
+	01-extended-auth-continue.cpp \
+	01-extended-auth-failure.cpp \
 	01-keepalive-pingreq.cpp \
 	01-no-clean-session.cpp \
 	01-pre-connect-callback.cpp \
diff --git a/test/lib/test.py b/test/lib/test.py
index a8ac951e..ee29a18b 100755
--- a/test/lib/test.py
+++ b/test/lib/test.py
@@ -9,6 +9,8 @@ tests = [
     (1, './01-con-discon-will-clear.py'),
     (1, './01-con-discon-will-v5.py'),
     (1, './01-con-discon-will.py'),
+    (1, './01-extended-auth-complete.py'),
+    (1, './01-extended-auth-failure.py'),
     (1, './01-keepalive-pingreq.py'),
     (1, './01-no-clean-session.py'),
     (1, './01-server-keepalive-pingreq.py'),