diff --git a/ChangeLog.txt b/ChangeLog.txt
index a04172e3..1a802369 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -18,6 +18,7 @@ Broker:
 - Report on what compile time options are enabled. Closes #2193.
 - Add `--tls-keylog` option which can be used to generate a file that can be
   used by wireshark to decrypt TLS traffic for debugging purposes. Closes #1818.
+- Add support for delayed basic authentication in plugins.
 
 Client library:
 - Add MOSQ_OPT_DISABLE_SOCKETPAIR to allow the disabling of the socketpair
diff --git a/include/mosquitto.h b/include/mosquitto.h
index 03557639..46237e05 100644
--- a/include/mosquitto.h
+++ b/include/mosquitto.h
@@ -85,6 +85,7 @@ extern "C" {
 
 /* Error values */
 enum mosq_err_t {
+	MOSQ_ERR_AUTH_DELAYED = -5,
 	MOSQ_ERR_AUTH_CONTINUE = -4,
 	MOSQ_ERR_NO_SUBSCRIBERS = -3,
 	MOSQ_ERR_SUB_EXISTS = -2,
diff --git a/include/mosquitto_broker.h b/include/mosquitto_broker.h
index 631dc34f..6f818a96 100644
--- a/include/mosquitto_broker.h
+++ b/include/mosquitto_broker.h
@@ -592,4 +592,29 @@ mosq_EXPORT int mosquitto_broker_publish_copy(
 }
 #endif
 
+/* Function: mosquitto_complete_basic_auth
+ *
+ * Complete a delayed authentication request.
+ *
+ * Useful for plugins that subscribe to the MOSQ_EVT_BASIC_AUTH event. If your
+ * plugin makes authentication requests that are not "instant", in particular
+ * if they communicate with an external service, then instead of blocking for a
+ * reply and returning MOSQ_ERR_SUCCESS or MOSQ_ERR_AUTH, the plugin can return
+ * MOSQ_ERR_AUTH_DELAYED. This means that the plugin is promising to tell the
+ * broker the authentication result in the future. Once the plugin has an
+ * answer, it should call `mosquitto_complete_basic_auth()` passing the client
+ * id and the result.
+ *
+ * Result:
+ *  MOSQ_ERR_SUCCESS - the client successfully authenticated
+ *  MOSQ_ERR_AUTH - the client authentication failed
+ *
+ * Other error codes can be used if more appropriate, and the client connection
+ * will still be rejected, e.g. MOSQ_ERR_NOMEM.
+ *
+ * The plugin may use extra threads to handle the authentication requests, but
+ * the call to `mosquitto_complete_basic_auth()` must happen in the main
+ * mosquitto thread. Using the MOSQ_EVT_TICK event for this is suggested.
+ */
+void mosquitto_complete_basic_auth(const char *client_id, int result);
 #endif
diff --git a/lib/mosquitto_internal.h b/lib/mosquitto_internal.h
index 4c9779b7..432e6c5a 100644
--- a/lib/mosquitto_internal.h
+++ b/lib/mosquitto_internal.h
@@ -114,6 +114,7 @@ enum mosquitto_client_state {
 	mosq_cs_disused = 19, /* client that has been added to the disused list to be freed */
 	mosq_cs_authenticating = 20, /* Client has sent CONNECT but is still undergoing extended authentication */
 	mosq_cs_reauthenticating = 21, /* Client is undergoing reauthentication and shouldn't do anything else until complete */
+	mosq_cs_delayed_auth = 22, /* Client is awaiting an authentication result from a plugin */
 };
 
 enum mosquitto__protocol {
diff --git a/plugins/README.md b/plugins/README.md
index 6c63c915..efea0c61 100644
--- a/plugins/README.md
+++ b/plugins/README.md
@@ -26,6 +26,14 @@ disconnect events. It publishes messages to
 $SYS/broker/connection/client/<client id>/state for every client that connects
 to the broker, to indicate the connection state of that client.
 
+## Examples / Deferred authentication
+This is an **example** plugin to demonstrate how a plugin can carry out
+delayed basic authentication. This method should be used where the plugin
+sends an authentication request to an external server so that if there is a
+delay in getting a response it does not block the broker. The plugin may spawn
+extra threads to handle the authentication requests, but the call to
+`mosquitto_complete_basic_auth()` must happen in the main Mosquitto thread.
+
 ## Examples / Message timestamp
 This is an **example** plugin to demonstrate how it is possible to attach MQTT
 v5 properties to messages after they have been received, and before they are
diff --git a/plugins/examples/CMakeLists.txt b/plugins/examples/CMakeLists.txt
index ff51dfba..b75b228b 100644
--- a/plugins/examples/CMakeLists.txt
+++ b/plugins/examples/CMakeLists.txt
@@ -5,4 +5,5 @@ endif()
 add_subdirectory(auth-by-ip)
 add_subdirectory(client-properties)
 add_subdirectory(connection-state)
+add_subdirectory(delayed-auth)
 add_subdirectory(payload-modification)
diff --git a/plugins/examples/Makefile b/plugins/examples/Makefile
index 9fd0e665..0a007958 100644
--- a/plugins/examples/Makefile
+++ b/plugins/examples/Makefile
@@ -3,6 +3,7 @@ DIRS= \
 		auth-by-ip \
 		client-properties \
 		connection-state \
+		delayed-auth \
 		message-timestamp \
 		payload-modification
 
diff --git a/plugins/examples/delayed-auth/CMakeLists.txt b/plugins/examples/delayed-auth/CMakeLists.txt
new file mode 100644
index 00000000..9f96436c
--- /dev/null
+++ b/plugins/examples/delayed-auth/CMakeLists.txt
@@ -0,0 +1,18 @@
+add_library(mosquitto_delayed_auth SHARED
+	mosquitto_delayed_auth.c
+)
+
+target_include_directories(mosquitto_delayed_auth PRIVATE
+	"${STDBOOL_H_PATH}"
+	"${STDINT_H_PATH}"
+	"${mosquitto_SOURCE_DIR}"
+	"${mosquitto_SOURCE_DIR}/include"
+)
+
+set_target_properties(mosquitto_delayed_auth PROPERTIES
+	PREFIX ""
+	POSITION_INDEPENDENT_CODE 1
+)
+
+# Don't install, these are example plugins only.
+#install(TARGETS mosquitto_delayed_auth RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}" LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}")
diff --git a/plugins/examples/delayed-auth/Makefile b/plugins/examples/delayed-auth/Makefile
new file mode 100644
index 00000000..f038e066
--- /dev/null
+++ b/plugins/examples/delayed-auth/Makefile
@@ -0,0 +1,28 @@
+include ../../../config.mk
+
+.PHONY : all binary check clean reallyclean test install uninstall
+
+PLUGIN_NAME=mosquitto_delayed_auth
+PLUGIN_CFLAGS+=-I../../../include -I../../../
+
+all : binary
+
+binary : ${PLUGIN_NAME}.so
+
+${PLUGIN_NAME}.so : ${PLUGIN_NAME}.c
+	$(CROSS_COMPILE)$(CC) $(PLUGIN_CPPFLAGS) $(PLUGIN_CFLAGS) $(PLUGIN_LDFLAGS) -fPIC -shared $< -o $@
+
+reallyclean : clean
+clean:
+	-rm -f *.o ${PLUGIN_NAME}.so *.gcda *.gcno
+
+check: test
+test:
+
+install: ${PLUGIN_NAME}.so
+	# Don't install, these are examples only.
+	#$(INSTALL) -d "${DESTDIR}$(libdir)"
+	#$(INSTALL) ${STRIP_OPTS} ${PLUGIN_NAME}.so "${DESTDIR}${libdir}/${PLUGIN_NAME}.so"
+
+uninstall :
+	-rm -f "${DESTDIR}${libdir}/${PLUGIN_NAME}.so"
diff --git a/plugins/examples/delayed-auth/mosquitto_delayed_auth.c b/plugins/examples/delayed-auth/mosquitto_delayed_auth.c
new file mode 100644
index 00000000..92c26265
--- /dev/null
+++ b/plugins/examples/delayed-auth/mosquitto_delayed_auth.c
@@ -0,0 +1,176 @@
+/*
+Copyright (c) 2021 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 EDL-1.0
+
+Contributors:
+   Roger Light - initial implementation and documentation.
+*/
+
+/*
+ * This is an example plugin showing how to carry out delayed authentication.
+ * The "authentication" in this example makes no checks whatsoever, but delays
+ * the response by 5 seconds, and randomly chooses whether it should succeed.
+ *
+ * Compile with:
+ *   gcc -I<path to mosquitto-repo/include> -fPIC -shared mosquitto_delayed_auth.c -o mosquitto_delayed_auth.so
+ *
+ * Use in config with:
+ *
+ *   plugin /path/to/mosquitto_delayed_auth.so
+ *
+ * Note that this only works on Mosquitto 2.0 or later.
+ */
+
+
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+#include <uthash.h>
+
+#include "mosquitto_broker.h"
+#include "mosquitto_plugin.h"
+#include "mosquitto.h"
+#include "mqtt_protocol.h"
+
+#ifndef UNUSED
+#  define UNUSED(A) (void)(A)
+#endif
+
+struct client_list{
+	UT_hash_handle hh;
+	char *id;
+	time_t request_time;
+};
+
+static mosquitto_plugin_id_t *mosq_pid = NULL;
+static struct client_list *clients = NULL;
+static time_t last_check = 0;
+
+bool authentication_check(struct client_list *client, time_t now)
+{
+	time_t secs;
+
+	secs = now - client->request_time;
+
+	return secs > 5 ? true : false;
+}
+
+static int basic_auth_callback(int event, void *event_data, void *userdata)
+{
+	struct mosquitto_evt_basic_auth *ed = event_data;
+	static struct client_list *client;
+	const char *id;
+
+	UNUSED(event);
+	UNUSED(userdata);
+
+	id = mosquitto_client_id(ed->client);
+
+	HASH_FIND(hh, clients, id, strlen(id), client);
+	if(client){
+		client->request_time = time(NULL);
+	}else{
+		client = mosquitto_malloc(sizeof(struct client_list));
+		if(client == NULL){
+			return MOSQ_ERR_NOMEM;
+		}
+
+		client->id = mosquitto_strdup(id);
+		if(client->id == NULL){
+			mosquitto_free(client);
+			return MOSQ_ERR_NOMEM;
+		}
+		client->request_time = time(NULL);
+		HASH_ADD_KEYPTR(hh, clients, client->id, strlen(client->id), client);
+
+		mosquitto_log_printf(MOSQ_LOG_DEBUG, "Starting auth for %s at %d", client->id, time(NULL));
+	}
+
+	return MOSQ_ERR_AUTH_DELAYED;
+}
+
+
+static int tick_callback(int event, void *event_data, void *userdata)
+{
+	struct client_list *client, *client_tmp;
+	time_t now;
+	long r;
+
+	UNUSED(event);
+	UNUSED(event_data);
+	UNUSED(userdata);
+
+	now = time(NULL);
+	if(now > last_check){
+		HASH_ITER(hh, clients, client, client_tmp){
+			if(authentication_check(client, now)){
+				/* Deny access 1/4 of the time, yes it's biased number generation. */
+				 r = random() % 1000;
+				if(r > 740){
+					mosquitto_complete_basic_auth(client->id, MOSQ_ERR_AUTH);
+				}else{
+					mosquitto_complete_basic_auth(client->id, MOSQ_ERR_SUCCESS);
+				}
+				mosquitto_log_printf(MOSQ_LOG_DEBUG, "Completing auth for %s at %d", client->id, now);
+				HASH_DELETE(hh, clients, client);
+				mosquitto_free(client->id);
+				mosquitto_free(client);
+			}
+		}
+		last_check = now;
+	}
+	return MOSQ_ERR_SUCCESS;
+}
+
+
+int mosquitto_plugin_version(int supported_version_count, const int *supported_versions)
+{
+	int i;
+
+	for(i=0; i<supported_version_count; i++){
+		if(supported_versions[i] == 5){
+			return 5;
+		}
+	}
+	return -1;
+}
+
+int mosquitto_plugin_init(mosquitto_plugin_id_t *identifier, void **user_data, struct mosquitto_opt *opts, int opt_count)
+{
+	int rc;
+
+	UNUSED(user_data);
+	UNUSED(opts);
+	UNUSED(opt_count);
+
+	mosq_pid = identifier;
+
+	rc = mosquitto_callback_register(mosq_pid, MOSQ_EVT_BASIC_AUTH, basic_auth_callback, NULL, NULL);
+	if(rc) return rc;
+	rc = mosquitto_callback_register(mosq_pid, MOSQ_EVT_TICK, tick_callback, NULL, NULL);
+	return rc;
+}
+
+int mosquitto_plugin_cleanup(void *user_data, struct mosquitto_opt *opts, int opt_count)
+{
+	UNUSED(user_data);
+	UNUSED(opts);
+	UNUSED(opt_count);
+
+	mosquitto_callback_unregister(mosq_pid, MOSQ_EVT_BASIC_AUTH, basic_auth_callback, NULL);
+	mosquitto_callback_unregister(mosq_pid, MOSQ_EVT_TICK, tick_callback, NULL);
+
+	return 0;
+}
diff --git a/plugins/examples/delayed-auth/test.conf b/plugins/examples/delayed-auth/test.conf
new file mode 100644
index 00000000..81a32458
--- /dev/null
+++ b/plugins/examples/delayed-auth/test.conf
@@ -0,0 +1,7 @@
+listener 1883
+
+plugin ./mosquitto_delayed_auth.so
+
+
+sys_interval 1
+log_timestamp_format %Y-%m-%dT%H:%M:%S
diff --git a/plugins/examples/delayed-auth/test.sh b/plugins/examples/delayed-auth/test.sh
new file mode 100755
index 00000000..75a50f90
--- /dev/null
+++ b/plugins/examples/delayed-auth/test.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+../../src/mosquitto -c test.conf -v
diff --git a/src/context.c b/src/context.c
index 7e8ecc6a..6e580c54 100644
--- a/src/context.c
+++ b/src/context.c
@@ -69,8 +69,8 @@ struct mosquitto *context__init(void)
 	mosquitto__set_state(context, mosq_cs_new);
 	context->sock = INVALID_SOCKET;
 	context->last_msg_in = db.now_s;
-	context->next_msg_out = db.now_s + 60;
-	context->keepalive = 60; /* Default to 60s */
+	context->next_msg_out = db.now_s + 20;
+	context->keepalive = 20; /* Default to 20s */
 	context->clean_start = true;
 	context->id = NULL;
 	context->last_mid = 0;
@@ -294,6 +294,11 @@ void context__remove_from_by_id(struct mosquitto *context)
 	struct mosquitto *context_found;
 
 	if(context->removed_from_by_id == false && context->id){
+		HASH_FIND(hh_id, db.contexts_by_id_delayed_auth, context->id, strlen(context->id), context_found);
+		if(context_found){
+			HASH_DELETE(hh_id, db.contexts_by_id_delayed_auth, context_found);
+		}
+
 		HASH_FIND(hh_id, db.contexts_by_id, context->id, strlen(context->id), context_found);
 		if(context_found){
 			HASH_DELETE(hh_id, db.contexts_by_id, context_found);
diff --git a/src/handle_connect.c b/src/handle_connect.c
index ecd7ade8..eeddf7f3 100644
--- a/src/handle_connect.c
+++ b/src/handle_connect.c
@@ -406,6 +406,7 @@ int handle__connect(struct mosquitto *context)
 	uint8_t protocol_version;
 	uint8_t connect_flags;
 	char *client_id = NULL;
+	struct mosquitto *found_context;
 	struct mosquitto_message_all *will_struct = NULL;
 	uint8_t will, will_retain, will_qos, clean_start;
 	uint8_t username_flag, password_flag;
@@ -629,6 +630,13 @@ int handle__connect(struct mosquitto *context)
 		}
 	}
 
+	/* Check for an existing delayed auth check, reject if present */
+	HASH_FIND(hh_id, db.contexts_by_id_delayed_auth, client_id, strlen(client_id), found_context);
+	if(found_context){
+		rc = MOSQ_ERR_UNKNOWN;
+		goto handle_connect_error;
+	}
+
 	if(will){
 		rc = will__read(context, client_id, &will_struct, will_qos, will_retain);
 		if(rc) goto handle_connect_error;
@@ -889,7 +897,7 @@ int handle__connect(struct mosquitto *context)
 #endif
 		{
 			rc = mosquitto_unpwd_check(context);
-			if(rc != MOSQ_ERR_SUCCESS){
+			if(rc != MOSQ_ERR_SUCCESS && rc != MOSQ_ERR_AUTH_DELAYED){
 				/* We must have context->id == NULL here so we don't later try and
 				* remove the client from the by_id hash table */
 				mosquitto__free(context->id);
@@ -898,6 +906,11 @@ int handle__connect(struct mosquitto *context)
 			switch(rc){
 				case MOSQ_ERR_SUCCESS:
 					break;
+				case MOSQ_ERR_AUTH_DELAYED:
+					mosquitto__set_state(context, mosq_cs_delayed_auth);
+					HASH_ADD_KEYPTR(hh_id, db.contexts_by_id_delayed_auth, context->id, strlen(context->id), context);
+					return MOSQ_ERR_SUCCESS;
+					break;
 				case MOSQ_ERR_AUTH:
 					if(context->protocol == mosq_p_mqtt5){
 						send__connack(context, 0, MQTT_RC_NOT_AUTHORIZED, NULL);
diff --git a/src/linker-macosx.syms b/src/linker-macosx.syms
index bbd9136a..dddda52c 100644
--- a/src/linker-macosx.syms
+++ b/src/linker-macosx.syms
@@ -12,6 +12,7 @@ _mosquitto_client_protocol
 _mosquitto_client_protocol_version
 _mosquitto_client_sub_count
 _mosquitto_client_username
+_mosquitto_complete_basic_auth
 _mosquitto_free
 _mosquitto_kick_client_by_clientid
 _mosquitto_kick_client_by_username
diff --git a/src/linker.syms b/src/linker.syms
index 753d00aa..5792bc06 100644
--- a/src/linker.syms
+++ b/src/linker.syms
@@ -13,6 +13,7 @@
 	mosquitto_client_protocol_version;
 	mosquitto_client_sub_count;
 	mosquitto_client_username;
+	mosquitto_complete_basic_auth;
 	mosquitto_free;
 	mosquitto_kick_client_by_clientid;
 	mosquitto_kick_client_by_username;
diff --git a/src/mosquitto_broker_internal.h b/src/mosquitto_broker_internal.h
index f5067288..4a2bc939 100644
--- a/src/mosquitto_broker_internal.h
+++ b/src/mosquitto_broker_internal.h
@@ -445,6 +445,7 @@ struct mosquitto_db{
 	struct mosquitto__retainhier *retains;
 	struct mosquitto *contexts_by_id;
 	struct mosquitto *contexts_by_sock;
+	struct mosquitto *contexts_by_id_delayed_auth;
 	struct mosquitto *contexts_for_free;
 #ifdef WITH_BRIDGE
 	struct mosquitto **bridges;
diff --git a/src/plugin.c b/src/plugin.c
index d45ed78c..92f69ac1 100644
--- a/src/plugin.c
+++ b/src/plugin.c
@@ -27,6 +27,7 @@ Contributors:
 #include "util_mosq.h"
 #include "utlist.h"
 #include "lib_load.h"
+#include "will_mosq.h"
 
 
 static bool check_callback_exists(struct mosquitto__callback *cb_base, MOSQ_FUNC_generic_callback cb_func)
@@ -345,3 +346,28 @@ int mosquitto_callback_unregister(
 
 	return remove_callback(cb_base, cb_func);
 }
+
+void mosquitto_complete_basic_auth(const char *client_id, int result)
+{
+	struct mosquitto *context;
+
+	if(client_id == NULL) return;
+
+	HASH_FIND(hh_id, db.contexts_by_id_delayed_auth, client_id, strlen(client_id), context);
+	if(context){
+		HASH_DELETE(hh_id, db.contexts_by_id_delayed_auth, context);
+		if(result == MOSQ_ERR_SUCCESS){
+			connect__on_authorised(context, NULL, 0);
+		}else{
+			if(context->protocol == mosq_p_mqtt5){
+				send__connack(context, 0, MQTT_RC_NOT_AUTHORIZED, NULL);
+			}else{
+				send__connack(context, 0, CONNACK_REFUSED_NOT_AUTHORIZED, NULL);
+			}
+			context->clean_start = true;
+			context->session_expiry_interval = 0;
+			will__clear(context);
+			do_disconnect(context, MOSQ_ERR_AUTH);
+		}
+	}
+}
diff --git a/test/broker/09-plugin-delayed-auth.py b/test/broker/09-plugin-delayed-auth.py
new file mode 100755
index 00000000..95c8bf45
--- /dev/null
+++ b/test/broker/09-plugin-delayed-auth.py
@@ -0,0 +1,49 @@
+#!/usr/bin/env python3
+
+# Test whether message parameters are passed to the plugin acl check function.
+
+from mosq_test_helper import *
+
+def write_config(filename, port):
+    with open(filename, 'w') as f:
+        f.write("listener %d\n" % (port))
+        f.write("auth_plugin c/auth_plugin_delayed.so\n")
+        f.write("allow_anonymous false\n")
+
+def do_test(proto_ver):
+    port = mosq_test.get_port()
+    conf_file = os.path.basename(__file__).replace('.py', '.conf')
+    write_config(conf_file, port)
+
+    rc = 1
+    connect_packet = mosq_test.gen_connect("delayed-auth-test", keepalive=42, username="delayed-username", password="good", proto_ver=proto_ver)
+    connack_packet = mosq_test.gen_connack(rc=0, proto_ver=proto_ver)
+
+    connect_packet2 = mosq_test.gen_connect("delayed-auth-test", keepalive=42, username="delayed-username", password="bad", proto_ver=proto_ver)
+    if proto_ver == 5:
+        connack_packet2 = mosq_test.gen_connack(rc=mqtt5_rc.MQTT_RC_NOT_AUTHORIZED, proto_ver=proto_ver, property_helper=False)
+    else:
+        connack_packet2 = mosq_test.gen_connack(rc=5, proto_ver=proto_ver)
+
+    broker = mosq_test.start_broker(filename=os.path.basename(__file__), use_conf=True, port=port)
+
+    try:
+        sock = mosq_test.do_client_connect(connect_packet, connack_packet, timeout=20, port=port)
+        sock.close()
+        sock = mosq_test.do_client_connect(connect_packet2, connack_packet2, timeout=20, port=port)
+        rc = 0
+
+        sock.close()
+    except mosq_test.TestError:
+        pass
+    finally:
+        os.remove(conf_file)
+        broker.terminate()
+        broker.wait()
+        (stdo, stde) = broker.communicate()
+        if rc:
+            print(stde.decode('utf-8'))
+            exit(rc)
+
+do_test(4)
+do_test(5)
diff --git a/test/broker/Makefile b/test/broker/Makefile
index fad0f00b..0cce1a0a 100644
--- a/test/broker/Makefile
+++ b/test/broker/Makefile
@@ -194,6 +194,7 @@ endif
 	./09-plugin-auth-unpwd-success.py
 	./09-plugin-auth-v2-unpwd-fail.py
 	./09-plugin-auth-v2-unpwd-success.py
+	./09-plugin-delayed-auth.py
 	./09-plugin-publish.py
 	./09-pwfile-parse-invalid.py
 
diff --git a/test/broker/c/Makefile b/test/broker/c/Makefile
index 6a561ba1..f4e980be 100644
--- a/test/broker/c/Makefile
+++ b/test/broker/c/Makefile
@@ -3,19 +3,20 @@
 CFLAGS=-I../../../include -Wall -Werror
 
 PLUGIN_SRC = \
-	auth_plugin_v4.c \
-	auth_plugin_v5.c \
-	auth_plugin_v5_handle_message.c \
-	auth_plugin_pwd.c \
 	auth_plugin_acl.c \
 	auth_plugin_acl_sub_denied.c \
-	auth_plugin_v2.c \
 	auth_plugin_context_params.c \
-	auth_plugin_msg_params.c \
+	auth_plugin_delayed.c \
 	auth_plugin_extended_multiple.c \
 	auth_plugin_extended_single.c \
 	auth_plugin_extended_single2.c \
+	auth_plugin_msg_params.c \
 	auth_plugin_publish.c \
+	auth_plugin_pwd.c \
+	auth_plugin_v2.c \
+	auth_plugin_v4.c \
+	auth_plugin_v5.c \
+	auth_plugin_v5_handle_message.c \
 	plugin_control.c
 
 PLUGINS = ${PLUGIN_SRC:.c=.so}
diff --git a/test/broker/c/auth_plugin_delayed.c b/test/broker/c/auth_plugin_delayed.c
new file mode 100644
index 00000000..0a81dfea
--- /dev/null
+++ b/test/broker/c/auth_plugin_delayed.c
@@ -0,0 +1,94 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <mosquitto.h>
+#include <mosquitto_broker.h>
+#include <mosquitto_plugin.h>
+
+static int tick_callback(int event, void *event_data, void *user_data);
+static int unpwd_check_callback(int event, void *event_data, void *user_data);
+
+static mosquitto_plugin_id_t *plg_id;
+
+static char *username = NULL;
+static char *password = NULL;
+static char *client_id = NULL;
+static int auth_delay = -1;
+
+int mosquitto_plugin_version(int supported_version_count, const int *supported_versions)
+{
+	int i;
+
+	for(i=0; i<supported_version_count; i++){
+		if(supported_versions[i] == 5){
+			return 5;
+		}
+	}
+	return -1;
+}
+
+int mosquitto_plugin_init(mosquitto_plugin_id_t *identifier, void **user_data, struct mosquitto_opt *auth_opts, int auth_opt_count)
+{
+	plg_id = identifier;
+
+	mosquitto_callback_register(plg_id, MOSQ_EVT_TICK, tick_callback, NULL, NULL);
+	mosquitto_callback_register(plg_id, MOSQ_EVT_BASIC_AUTH, unpwd_check_callback, NULL, NULL);
+
+	return MOSQ_ERR_SUCCESS;
+}
+
+int mosquitto_plugin_cleanup(void *user_data, struct mosquitto_opt *auth_opts, int auth_opt_count)
+{
+	free(username);
+	free(password);
+	free(client_id);
+
+	mosquitto_callback_unregister(plg_id, MOSQ_EVT_BASIC_AUTH, unpwd_check_callback, NULL);
+	mosquitto_callback_unregister(plg_id, MOSQ_EVT_TICK, tick_callback, NULL);
+
+	return MOSQ_ERR_SUCCESS;
+}
+
+static int tick_callback(int event, void *event_data, void *user_data)
+{
+	if(auth_delay == 0){
+		if(client_id && username && password
+			&& !strcmp(username, "delayed-username") && !strcmp(password, "good")){
+
+			mosquitto_complete_basic_auth(client_id, MOSQ_ERR_SUCCESS);
+		}else{
+			mosquitto_complete_basic_auth(client_id, MOSQ_ERR_AUTH);
+		}
+		free(username);
+		free(password);
+		free(client_id);
+		username = NULL;
+		password = NULL;
+		client_id = NULL;
+	}else if(auth_delay > 0){
+		auth_delay--;
+	}
+
+	return MOSQ_ERR_SUCCESS;
+}
+
+static int unpwd_check_callback(int event, void *event_data, void *user_data)
+{
+	struct mosquitto_evt_basic_auth *ed = event_data;
+
+	free(username);
+	free(password);
+	free(client_id);
+
+	if(ed->username){
+		username = strdup(ed->username);
+	}
+	if(ed->password){
+		password = strdup(ed->password);
+	}
+	client_id = strdup(mosquitto_client_id(ed->client));
+	/* Delay for arbitrary 10 ticks */
+	auth_delay = 10;
+
+	return MOSQ_ERR_AUTH_DELAYED;
+}
diff --git a/test/broker/test.py b/test/broker/test.py
index a535d2f3..667899fb 100755
--- a/test/broker/test.py
+++ b/test/broker/test.py
@@ -167,6 +167,7 @@ tests = [
     (1, './09-plugin-auth-unpwd-success.py'),
     (1, './09-plugin-auth-v2-unpwd-fail.py'),
     (1, './09-plugin-auth-v2-unpwd-success.py'),
+    (1, './09-plugin-delayed-auth.py'),
     (1, './09-plugin-publish.py'),
     (1, './09-pwfile-parse-invalid.py'),
 
diff --git a/test/mosq_test.py b/test/mosq_test.py
index 91134ff4..c468e2c6 100644
--- a/test/mosq_test.py
+++ b/test/mosq_test.py
@@ -274,8 +274,15 @@ def to_string(packet):
         return s
     elif cmd == 0x20:
         # CONNACK
-        (cmd, rl, resv, rc) = struct.unpack('!BBBB', packet)
-        return "CONNACK, rl="+str(rl)+", res="+str(resv)+", rc="+str(rc)
+        if len(packet) == 4:
+            (cmd, rl, resv, rc) = struct.unpack('!BBBB', packet)
+            return "CONNACK, rl="+str(rl)+", res="+str(resv)+", rc="+str(rc)
+        elif len(packet) == 5:
+            (cmd, rl, flags, reason_code, proplen) = struct.unpack('!BBBBB', packet)
+            return "CONNACK, rl="+str(rl)+", flags="+str(flags)+", rc="+str(reason_code)+", proplen="+str(proplen)
+        else:
+            return "CONNACK, (not decoded)"
+
     elif cmd == 0x30:
         # PUBLISH
         dup = (packet0 & 0x08)>>3