diff --git a/apps/mosquitto_ctrl/broker.c b/apps/mosquitto_ctrl/broker.c
index 7fea7b64..805c7509 100644
--- a/apps/mosquitto_ctrl/broker.c
+++ b/apps/mosquitto_ctrl/broker.c
@@ -44,7 +44,7 @@ void broker__print_usage(void)
 static void print_listeners(cJSON *j_response)
 {
 	cJSON *j_data, *j_listeners, *j_listener, *jtmp;
-	char *stmp;
+	const char *stmp;
 	int i=1;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
@@ -89,7 +89,7 @@ static void print_listeners(cJSON *j_response)
 static void print_plugin_info(cJSON *j_response)
 {
 	cJSON *j_data, *j_plugins, *j_plugin, *jtmp, *j_eps;
-	char *stmp;
+	const char *stmp;
 	bool first;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
@@ -171,7 +171,7 @@ static void broker__payload_callback(struct mosq_ctrl *ctrl, long payloadlen, co
 		return;
 	}
 
-	char *error;
+	const char *error;
 	if(json_get_string(j_response, "error", &error, false) == MOSQ_ERR_SUCCESS){
 		fprintf(stderr, "%s: Error: %s.\n", j_command->valuestring, error);
 	}else{
diff --git a/apps/mosquitto_ctrl/dynsec.c b/apps/mosquitto_ctrl/dynsec.c
index 151b5c74..91efb0d4 100644
--- a/apps/mosquitto_ctrl/dynsec.c
+++ b/apps/mosquitto_ctrl/dynsec.c
@@ -116,7 +116,7 @@ static void print_list(cJSON *j_response, const char *arrayname, const char *key
 	}
 
 	cJSON_ArrayForEach(j_elem, j_array){
-		char *stmp;
+		const char *stmp;
 
 		if(cJSON_IsObject(j_elem)){
 			if(json_get_string(j_elem, keyname, &stmp, false) == MOSQ_ERR_SUCCESS){
@@ -152,7 +152,7 @@ static void print_json_array(cJSON *j_list, int slen, const char *label, const c
 	if(j_list && cJSON_IsArray(j_list)){
 		cJSON_ArrayForEach(j_elem, j_list){
 			if(cJSON_IsObject(j_elem)){
-				char *stmp;
+				const char *stmp;
 
 				if(json_get_string(j_elem, element_name, &stmp, false) != MOSQ_ERR_SUCCESS){
 					continue;
@@ -179,7 +179,7 @@ static void print_client(cJSON *j_response)
 {
 	cJSON *j_data, *j_client, *jtmp;
 	const int label_width = strlen( "Connections:");
-	char *stmp;
+	const char *stmp;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
 	if(j_data == NULL || !cJSON_IsObject(j_data)){
@@ -220,7 +220,7 @@ static void print_group(cJSON *j_response)
 {
 	cJSON *j_data, *j_group;
 	int label_width = strlen("Groupname:");
-	char *groupname;
+	const char *groupname;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
 	if(j_data == NULL || !cJSON_IsObject(j_data)){
@@ -249,7 +249,7 @@ static void print_role(cJSON *j_response)
 {
 	cJSON *j_data, *j_role, *j_array, *j_elem, *jtmp;
 	bool first;
-	char *stmp;
+	const char *stmp;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
 	if(j_data == NULL || !cJSON_IsObject(j_data)){
@@ -273,7 +273,7 @@ static void print_role(cJSON *j_response)
 	if(j_array && cJSON_IsArray(j_array)){
 		first = true;
 		cJSON_ArrayForEach(j_elem, j_array){
-			char *stmp;
+			const char *stmp;
 
 			if(json_get_string(j_role, "rolename", &stmp, false) == MOSQ_ERR_SUCCESS){
 				if(first){
@@ -306,7 +306,7 @@ static void print_role(cJSON *j_response)
 static void print_anonymous_group(cJSON *j_response)
 {
 	cJSON *j_data, *j_group;
-	char *groupname;
+	const char *groupname;
 
 	j_data = cJSON_GetObjectItem(j_response, "data");
 	if(j_data == NULL || !cJSON_IsObject(j_data)){
@@ -344,7 +344,7 @@ static void print_default_acl_access(cJSON *j_response)
 	}
 
 	cJSON_ArrayForEach(j_acl, j_acls){
-		char *acltype;
+		const char *acltype;
 		bool allow;
 
 		if(json_get_string(j_acl, "acltype", &acltype, false) != MOSQ_ERR_SUCCESS
@@ -360,7 +360,7 @@ static void print_default_acl_access(cJSON *j_response)
 static void dynsec__payload_callback(struct mosq_ctrl *ctrl, long payloadlen, const void *payload)
 {
 	cJSON *tree, *j_responses, *j_response;
-	char *command, *error;
+	const char *command, *error;
 
 	UNUSED(ctrl);
 
diff --git a/apps/mosquitto_ctrl/dynsec_client.c b/apps/mosquitto_ctrl/dynsec_client.c
index d1498b05..68486702 100644
--- a/apps/mosquitto_ctrl/dynsec_client.c
+++ b/apps/mosquitto_ctrl/dynsec_client.c
@@ -231,7 +231,7 @@ int dynsec_client__file_set_password(int argc, char *argv[], const char *file)
 
 	cJSON_ArrayForEach(j_client, j_clients){
 		if(cJSON_IsObject(j_client) == true){
-			char *username_json;
+			const char *username_json;
 			if(json_get_string(j_client, "username", &username_json, false) == MOSQ_ERR_SUCCESS){
 				if(!strcmp(username_json, username)){
 					if(dynsec_auth__pw_hash(&client, password, client.pw.password_hash, sizeof(client.pw.password_hash), true) != MOSQ_ERR_SUCCESS){
diff --git a/common/base64_mosq.c b/common/base64_mosq.c
index 8aff1473..461e9107 100644
--- a/common/base64_mosq.c
+++ b/common/base64_mosq.c
@@ -36,7 +36,7 @@ Contributors:
 #include "memory_mosq.h"
 
 #ifdef WITH_TLS
-int base64__encode(unsigned char *in, size_t in_len, char **encoded)
+int base64__encode(const unsigned char *in, size_t in_len, char **encoded)
 {
 	BIO *bmem, *b64;
 	BUF_MEM *bptr = NULL;
@@ -70,7 +70,7 @@ int base64__encode(unsigned char *in, size_t in_len, char **encoded)
 }
 
 
-int base64__decode(char *in, unsigned char **decoded, unsigned int *decoded_len)
+int base64__decode(const char *in, unsigned char **decoded, unsigned int *decoded_len)
 {
 	BIO *bmem, *b64;
 	size_t slen;
diff --git a/common/base64_mosq.h b/common/base64_mosq.h
index 04a35422..c52273a2 100644
--- a/common/base64_mosq.h
+++ b/common/base64_mosq.h
@@ -18,7 +18,7 @@ Contributors:
 #ifndef BASE64_MOSQ_H
 #define BASE64_MOSQ_H
 
-int base64__encode(unsigned char *in, size_t in_len, char **encoded);
-int base64__decode(char *in, unsigned char **decoded, unsigned int *decoded_len);
+int base64__encode(const unsigned char *in, size_t in_len, char **encoded);
+int base64__decode(const char *in, unsigned char **decoded, unsigned int *decoded_len);
 
 #endif
diff --git a/common/json_help.c b/common/json_help.c
index 2ca35729..b8986b4f 100644
--- a/common/json_help.c
+++ b/common/json_help.c
@@ -73,7 +73,7 @@ int json_get_int(cJSON *json, const char *name, int *value, bool optional, int d
 }
 
 
-int json_get_string(cJSON *json, const char *name, char **value, bool optional)
+int json_get_string(cJSON *json, const char *name, const char **value, bool optional)
 {
 	cJSON *jtmp;
 
@@ -84,7 +84,11 @@ int json_get_string(cJSON *json, const char *name, char **value, bool optional)
 		if(cJSON_IsString(jtmp) == false){
 			return MOSQ_ERR_INVAL;
 		}
-		*value = jtmp->valuestring;
+		if(jtmp->valuestring){
+			*value = jtmp->valuestring;
+		}else{
+			*value = "";
+		}
 	}else{
 		if(optional == false){
 			return MOSQ_ERR_INVAL;
diff --git a/common/json_help.h b/common/json_help.h
index 86226853..9d28c7e3 100644
--- a/common/json_help.h
+++ b/common/json_help.h
@@ -23,7 +23,7 @@ Contributors:
 /* "optional==false" can also be taken to mean "only return success if the key exists and is valid" */
 int json_get_bool(cJSON *json, const char *name, bool *value, bool optional, bool default_value);
 int json_get_int(cJSON *json, const char *name, int *value, bool optional, int default_value);
-int json_get_string(cJSON *json, const char *name, char **value, bool optional);
+int json_get_string(cJSON *json, const char *name, const char **value, bool optional);
 
 cJSON *cJSON_AddIntToObject(cJSON * const object, const char * const name, long long number);
 cJSON *cJSON_CreateInt(int num);
diff --git a/plugins/dynamic-security/clients.c b/plugins/dynamic-security/clients.c
index b2df0fae..9fab903a 100644
--- a/plugins/dynamic-security/clients.c
+++ b/plugins/dynamic-security/clients.c
@@ -114,10 +114,10 @@ int dynsec_clients__config_load(struct dynsec__data *data, cJSON *tree)
 	unsigned int buf_len;
 	int priority;
 	int iterations;
-	char *username;
+	const char *username;
 	size_t username_len;
-	char *salt;
-	char *password;
+	const char *salt;
+	const char *password;
 
 	j_clients = cJSON_GetObjectItem(tree, "clients");
 	if(j_clients == NULL){
@@ -185,7 +185,7 @@ int dynsec_clients__config_load(struct dynsec__data *data, cJSON *tree)
 			}
 
 			/* Client id */
-			char *clientid;
+			const char *clientid;
 			if(json_get_string(j_client, "clientid", &clientid, false) == MOSQ_ERR_SUCCESS){
 				client->clientid = mosquitto_strdup(clientid);
 				if(client->clientid == NULL){
@@ -195,7 +195,7 @@ int dynsec_clients__config_load(struct dynsec__data *data, cJSON *tree)
 			}
 
 			/* Text name */
-			char *textname;
+			const char *textname;
 			if(json_get_string(j_client, "textname", &textname, false) == MOSQ_ERR_SUCCESS){
 				client->text_name = mosquitto_strdup(textname);
 				if(client->text_name == NULL){
@@ -206,7 +206,7 @@ int dynsec_clients__config_load(struct dynsec__data *data, cJSON *tree)
 			}
 
 			/* Text description */
-			char *textdescription;
+			const char *textdescription;
 			if(json_get_string(j_client, "textdescription", &textdescription, false) == MOSQ_ERR_SUCCESS){
 				client->text_description = mosquitto_strdup(textdescription);
 				if(client->text_description == NULL){
@@ -222,7 +222,7 @@ int dynsec_clients__config_load(struct dynsec__data *data, cJSON *tree)
 			if(j_roles && cJSON_IsArray(j_roles)){
 				cJSON_ArrayForEach(j_role, j_roles){
 					if(cJSON_IsObject(j_role)){
-						char *rolename;
+						const char *rolename;
 						if(json_get_string(j_role, "rolename", &rolename, false) == MOSQ_ERR_SUCCESS){
 							json_get_int(j_role, "priority", &priority, true, -1);
 							role = dynsec_roles__find(data, rolename);
@@ -313,8 +313,8 @@ int dynsec_clients__config_save(struct dynsec__data *data, cJSON *tree)
 
 int dynsec_clients__process_create(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *password, *clientid = NULL;
-	char *text_name, *text_description;
+	const char *username, *password, *clientid = NULL;
+	const char *text_name, *text_description;
 	struct dynsec__client *client;
 	int rc;
 	cJSON *j_groups, *j_group;
@@ -431,7 +431,7 @@ int dynsec_clients__process_create(struct dynsec__data *data, struct mosquitto_c
 	if(j_groups && cJSON_IsArray(j_groups)){
 		cJSON_ArrayForEach(j_group, j_groups){
 			if(cJSON_IsObject(j_group)){
-				char *groupname;
+				const char *groupname;
 				if(json_get_string(j_group, "groupname", &groupname, false) == MOSQ_ERR_SUCCESS){
 					json_get_int(j_group, "priority", &priority, true, -1);
 					rc = dynsec_groups__add_client(data, username, groupname, priority, false);
@@ -464,7 +464,7 @@ int dynsec_clients__process_create(struct dynsec__data *data, struct mosquitto_c
 
 int dynsec_clients__process_delete(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username;
+	const char *username;
 	struct dynsec__client *client;
 	const char *admin_clientid, *admin_username;
 
@@ -498,7 +498,7 @@ int dynsec_clients__process_delete(struct dynsec__data *data, struct mosquitto_c
 
 int dynsec_clients__process_disable(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username;
+	const char *username;
 	struct dynsec__client *client;
 	const char *admin_clientid, *admin_username;
 
@@ -535,7 +535,7 @@ int dynsec_clients__process_disable(struct dynsec__data *data, struct mosquitto_
 
 int dynsec_clients__process_enable(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username;
+	const char *username;
 	struct dynsec__client *client;
 	const char *admin_clientid, *admin_username;
 
@@ -570,7 +570,8 @@ int dynsec_clients__process_enable(struct dynsec__data *data, struct mosquitto_c
 
 int dynsec_clients__process_set_id(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *clientid, *clientid_heap = NULL;
+	const char *username, *clientid;
+	char *clientid_heap = NULL;
 	struct dynsec__client *client;
 	size_t slen;
 	const char *admin_clientid, *admin_username;
@@ -645,7 +646,7 @@ static int client__set_password(struct dynsec__client *client, const char *passw
 
 int dynsec_clients__process_set_password(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *password;
+	const char *username, *password;
 	struct dynsec__client *client;
 	int rc;
 	const char *admin_clientid, *admin_username;
@@ -712,15 +713,15 @@ static void client__remove_all_roles(struct dynsec__client *client)
 
 int dynsec_clients__process_modify(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username;
+	const char *username;
 	char *clientid = NULL;
-	char *password = NULL;
+	const char *password = NULL;
 	char *text_name = NULL, *text_description = NULL;
 	bool have_clientid = false, have_text_name = false, have_text_description = false, have_rolelist = false, have_password = false;
 	struct dynsec__client *client;
 	struct dynsec__group *group;
 	struct dynsec__rolelist *rolelist = NULL;
-	char *str;
+	const char *str;
 	int rc;
 	int priority;
 	cJSON *j_group, *j_groups;
@@ -805,7 +806,7 @@ int dynsec_clients__process_modify(struct dynsec__data *data, struct mosquitto_c
 		/* Iterate through list to check all groups are valid */
 		cJSON_ArrayForEach(j_group, j_groups){
 			if(cJSON_IsObject(j_group)){
-				char *groupname;
+				const char *groupname;
 				if(json_get_string(j_group, "groupname", &groupname, false) == MOSQ_ERR_SUCCESS){
 					group = dynsec_groups__find(data, groupname);
 					if(group == NULL){
@@ -824,7 +825,7 @@ int dynsec_clients__process_modify(struct dynsec__data *data, struct mosquitto_c
 		dynsec__remove_client_from_all_groups(data, username);
 		cJSON_ArrayForEach(j_group, j_groups){
 			if(cJSON_IsObject(j_group)){
-				char *groupname;
+				const char *groupname;
 				if(json_get_string(j_group, "groupname", &groupname, false) == MOSQ_ERR_SUCCESS){
 					json_get_int(j_group, "priority", &priority, true, -1);
 					dynsec_groups__add_client(data, username, groupname, priority, false);
@@ -1009,7 +1010,7 @@ static cJSON *add_client_to_json(struct dynsec__client *client, bool verbose)
 
 int dynsec_clients__process_get(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username;
+	const char *username;
 	struct dynsec__client *client;
 	cJSON *tree, *j_client, *j_data;
 	const char *admin_clientid, *admin_username;
@@ -1126,7 +1127,7 @@ int dynsec_clients__process_list(struct dynsec__data *data, struct mosquitto_con
 
 int dynsec_clients__process_add_role(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *rolename;
+	const char *username, *rolename;
 	struct dynsec__client *client;
 	struct dynsec__role *role;
 	int priority;
@@ -1184,7 +1185,7 @@ int dynsec_clients__process_add_role(struct dynsec__data *data, struct mosquitto
 
 int dynsec_clients__process_remove_role(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *rolename;
+	const char *username, *rolename;
 	struct dynsec__client *client;
 	struct dynsec__role *role;
 	const char *admin_clientid, *admin_username;
diff --git a/plugins/dynamic-security/default_acl.c b/plugins/dynamic-security/default_acl.c
index e806ece2..19eb147a 100644
--- a/plugins/dynamic-security/default_acl.c
+++ b/plugins/dynamic-security/default_acl.c
@@ -38,7 +38,7 @@ int dynsec__process_set_default_acl_access(struct dynsec__data *data, struct mos
 	cJSON *j_actions, *j_action;
 	bool allow;
 	const char *admin_clientid, *admin_username;
-	char *acltype;
+	const char *acltype;
 
 	j_actions = cJSON_GetObjectItem(cmd->j_command, "acls");
 	if(j_actions == NULL || !cJSON_IsArray(j_actions)){
diff --git a/plugins/dynamic-security/groups.c b/plugins/dynamic-security/groups.c
index 12e0315f..ec5986ec 100644
--- a/plugins/dynamic-security/groups.c
+++ b/plugins/dynamic-security/groups.c
@@ -104,7 +104,7 @@ static void group__free_item(struct dynsec__data *data, struct dynsec__group *gr
 
 int dynsec_groups__process_add_role(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname, *rolename;
+	const char *groupname, *rolename;
 	struct dynsec__group *group;
 	struct dynsec__role *role;
 	int priority;
@@ -195,8 +195,8 @@ int dynsec_groups__config_load(struct dynsec__data *data, cJSON *tree)
 	struct dynsec__group *group;
 	struct dynsec__role *role;
 	int priority;
-	char *textname, *textdescription;
-	char *groupname;
+	const char *textname, *textdescription;
+	const char *groupname;
 	size_t groupname_len;
 
 	j_groups = cJSON_GetObjectItem(tree, "groups");
@@ -258,7 +258,7 @@ int dynsec_groups__config_load(struct dynsec__data *data, cJSON *tree)
 
 				cJSON_ArrayForEach(j_role, j_roles){
 					if(cJSON_IsObject(j_role)){
-						char *rolename;
+						const char *rolename;
 						if(json_get_string(j_role, "rolename", &rolename, false) == MOSQ_ERR_SUCCESS){
 							json_get_int(j_role, "priority", &priority, true, -1);
 							role = dynsec_roles__find(data, rolename);
@@ -277,7 +277,7 @@ int dynsec_groups__config_load(struct dynsec__data *data, cJSON *tree)
 				cJSON *j_client;
 				cJSON_ArrayForEach(j_client, j_clientlist){
 					if(cJSON_IsObject(j_client)){
-						char *username;
+						const char *username;
 						if(json_get_string(j_client, "username", &username, false) == MOSQ_ERR_SUCCESS){
 							json_get_int(j_client, "priority", &priority, true, -1);
 							dynsec_groups__add_client(data, username, group->groupname, priority, false);
@@ -364,7 +364,7 @@ int dynsec_groups__config_save(struct dynsec__data *data, cJSON *tree)
 
 int dynsec_groups__process_create(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname, *text_name, *text_description;
+	const char *groupname, *text_name, *text_description;
 	struct dynsec__group *group = NULL;
 	int rc = MOSQ_ERR_SUCCESS;
 	const char *admin_clientid, *admin_username;
@@ -450,7 +450,7 @@ int dynsec_groups__process_create(struct dynsec__data *data, struct mosquitto_co
 
 int dynsec_groups__process_delete(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname;
+	const char *groupname;
 	struct dynsec__group *group;
 	const char *admin_clientid, *admin_username;
 
@@ -534,7 +534,7 @@ int dynsec_groups__add_client(struct dynsec__data *data, const char *username, c
 
 int dynsec_groups__process_add_client(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *groupname;
+	const char *username, *groupname;
 	int rc;
 	int priority;
 	const char *admin_clientid, *admin_username;
@@ -636,7 +636,7 @@ int dynsec_groups__remove_client(struct dynsec__data *data, const char *username
 
 int dynsec_groups__process_remove_client(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *username, *groupname;
+	const char *username, *groupname;
 	int rc;
 	const char *admin_clientid, *admin_username;
 
@@ -804,7 +804,7 @@ int dynsec_groups__process_list(struct dynsec__data *data, struct mosquitto_cont
 
 int dynsec_groups__process_get(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname;
+	const char *groupname;
 	cJSON *tree, *j_group, *j_data;
 	struct dynsec__group *group;
 	const char *admin_clientid, *admin_username;
@@ -862,7 +862,7 @@ int dynsec_groups__process_get(struct dynsec__data *data, struct mosquitto_contr
 
 int dynsec_groups__process_remove_role(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname, *rolename;
+	const char *groupname, *rolename;
 	struct dynsec__group *group;
 	struct dynsec__role *role;
 	const char *admin_clientid, *admin_username;
@@ -915,18 +915,17 @@ int dynsec_groups__process_remove_role(struct dynsec__data *data, struct mosquit
 
 int dynsec_groups__process_modify(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname = NULL;
+	const char *groupname = NULL;
 	char *text_name = NULL, *text_description = NULL;
 	struct dynsec__client *client = NULL;
 	struct dynsec__group *group = NULL;
 	struct dynsec__rolelist *rolelist = NULL;
 	bool have_text_name = false, have_text_description = false, have_rolelist = false;
-	char *str;
+	const char *str;
 	int rc;
 	int priority;
 	cJSON *j_client, *j_clients;
 	const char *admin_clientid, *admin_username;
-	char *username;
 
 	if(json_get_string(cmd->j_command, "groupname", &groupname, false) != MOSQ_ERR_SUCCESS){
 		mosquitto_control_command_reply(cmd, "Invalid/missing groupname");
@@ -986,6 +985,7 @@ int dynsec_groups__process_modify(struct dynsec__data *data, struct mosquitto_co
 
 	j_clients = cJSON_GetObjectItem(cmd->j_command, "clients");
 	if(j_clients && cJSON_IsArray(j_clients)){
+		const char *username;
 		/* Iterate over array to check clients are valid before proceeding */
 		cJSON_ArrayForEach(j_client, j_clients){
 			if(cJSON_IsObject(j_client)){
@@ -1065,7 +1065,7 @@ error:
 
 int dynsec_groups__process_set_anonymous_group(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *groupname;
+	const char *groupname;
 	struct dynsec__group *group = NULL;
 	const char *admin_clientid, *admin_username;
 
diff --git a/plugins/dynamic-security/rolelist.c b/plugins/dynamic-security/rolelist.c
index 1965eac4..71cc0389 100644
--- a/plugins/dynamic-security/rolelist.c
+++ b/plugins/dynamic-security/rolelist.c
@@ -174,7 +174,7 @@ int dynsec_rolelist__load_from_json(struct dynsec__data *data, cJSON *command, s
 	cJSON *j_roles, *j_role;
 	int priority;
 	struct dynsec__role *role;
-	char *rolename;
+	const char *rolename;
 
 	j_roles = cJSON_GetObjectItem(command, "roles");
 	if(j_roles){
diff --git a/plugins/dynamic-security/roles.c b/plugins/dynamic-security/roles.c
index 12168ba0..98b3976f 100644
--- a/plugins/dynamic-security/roles.c
+++ b/plugins/dynamic-security/roles.c
@@ -207,8 +207,8 @@ static int dynsec_roles__acl_load(cJSON *j_acls, const char *key, struct dynsec_
 	cJSON *j_acl, *jtmp;
 	struct dynsec__acl *acl;
 	size_t topic_len;
-	char *acltype;
-	char *topic;
+	const char *acltype;
+	const char *topic;
 
 	cJSON_ArrayForEach(j_acl, j_acls){
 		if(json_get_string(j_acl, "acltype", &acltype, false) != MOSQ_ERR_SUCCESS){
@@ -265,7 +265,7 @@ int dynsec_roles__config_load(struct dynsec__data *data, cJSON *tree)
 	cJSON_ArrayForEach(j_role, j_roles){
 		if(cJSON_IsObject(j_role) == true){
 			/* Role name */
-			char *rolename;
+			const char *rolename;
 			if(json_get_string(j_role, "rolename", &rolename, false) != MOSQ_ERR_SUCCESS){
 				continue;
 			}
@@ -284,7 +284,7 @@ int dynsec_roles__config_load(struct dynsec__data *data, cJSON *tree)
 			strncpy(role->rolename, rolename, rolename_len+1);
 
 			/* Text name */
-			char *textname;
+			const char *textname;
 			if(json_get_string(j_role, "textname", &textname, false) == MOSQ_ERR_SUCCESS){
 				role->text_name = mosquitto_strdup(textname);
 				if(role->text_name == NULL){
@@ -294,7 +294,7 @@ int dynsec_roles__config_load(struct dynsec__data *data, cJSON *tree)
 			}
 
 			/* Text description */
-			char *textdescription;
+			const char *textdescription;
 			if(json_get_string(j_role, "textdescription", &textdescription, false) == MOSQ_ERR_SUCCESS){
 				role->text_description = mosquitto_strdup(textdescription);
 				if(role->text_description == NULL){
@@ -339,8 +339,8 @@ int dynsec_roles__config_load(struct dynsec__data *data, cJSON *tree)
 
 int dynsec_roles__process_create(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *rolename;
-	char *text_name, *text_description;
+	const char *rolename;
+	const char *text_name, *text_description;
 	bool allow_wildcard_subs;
 	struct dynsec__role *role;
 	int rc = MOSQ_ERR_SUCCESS;
@@ -472,7 +472,7 @@ static void role__remove_all_groups(struct dynsec__data *data, struct dynsec__ro
 
 int dynsec_roles__process_delete(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *rolename;
+	const char *rolename;
 	struct dynsec__role *role;
 	const char *admin_clientid, *admin_username;
 
@@ -602,14 +602,14 @@ int dynsec_roles__process_list(struct dynsec__data *data, struct mosquitto_contr
 
 int dynsec_roles__process_add_acl(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *rolename;
+	const char *rolename;
 	struct dynsec__role *role;
 	struct dynsec__acl **acllist, *acl;
 	int rc;
 	const char *admin_clientid, *admin_username;
-	char *topic;
+	const char *topic;
 	size_t topic_len;
-	char *acltype;
+	const char *acltype;
 
 	if(json_get_string(cmd->j_command, "rolename", &rolename, false) != MOSQ_ERR_SUCCESS){
 		mosquitto_control_command_reply(cmd, "Invalid/missing rolename");
@@ -696,13 +696,13 @@ int dynsec_roles__process_add_acl(struct dynsec__data *data, struct mosquitto_co
 
 int dynsec_roles__process_remove_acl(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *rolename;
+	const char *rolename;
 	struct dynsec__role *role;
 	struct dynsec__acl **acllist, *acl;
-	char *topic;
+	const char *topic;
 	int rc;
 	const char *admin_clientid, *admin_username;
-	char *acltype;
+	const char *acltype;
 
 	if(json_get_string(cmd->j_command, "rolename", &rolename, false) != MOSQ_ERR_SUCCESS){
 		mosquitto_control_command_reply(cmd, "Invalid/missing rolename");
@@ -777,7 +777,7 @@ int dynsec_roles__process_remove_acl(struct dynsec__data *data, struct mosquitto
 
 int dynsec_roles__process_get(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *rolename;
+	const char *rolename;
 	struct dynsec__role *role;
 	cJSON *tree, *j_role, *j_data;
 	const char *admin_clientid, *admin_username;
@@ -833,8 +833,8 @@ int dynsec_roles__process_get(struct dynsec__data *data, struct mosquitto_contro
 
 int dynsec_roles__process_modify(struct dynsec__data *data, struct mosquitto_control_cmd *cmd, struct mosquitto *context)
 {
-	char *rolename;
-	char *text_name, *text_description;
+	const char *rolename;
+	const char *text_name, *text_description;
 	struct dynsec__role *role;
 	char *str;
 	cJSON *j_acls;
diff --git a/plugins/persist-sqlite/CMakeLists.txt b/plugins/persist-sqlite/CMakeLists.txt
index 043bde32..46034293 100644
--- a/plugins/persist-sqlite/CMakeLists.txt
+++ b/plugins/persist-sqlite/CMakeLists.txt
@@ -10,6 +10,7 @@ if(SQLITE3_FOUND AND CJSON_FOUND)
 		clients.c
 		client_msgs.c
 		init.c
+		../../common/json_help.c ../../common/json_help.h
 		plugin.c
 		restore.c
 		retain_msgs.c
diff --git a/plugins/persist-sqlite/Makefile b/plugins/persist-sqlite/Makefile
index ecc8e8b7..9465df8b 100644
--- a/plugins/persist-sqlite/Makefile
+++ b/plugins/persist-sqlite/Makefile
@@ -11,6 +11,7 @@ OBJS=	\
 		clients.o \
 		client_msgs.o \
 		init.o \
+		json_help.o \
 		plugin.o \
 		restore.o \
 		retain_msgs.o \
@@ -38,6 +39,9 @@ client_msgs.o : client_msgs.c persist_sqlite.h
 init.o : init.c persist_sqlite.h
 	${CROSS_COMPILE}${CC} $(LOCAL_CPPFLAGS) $(PLUGIN_CPPFLAGS) $(PLUGIN_CFLAGS) -c $< -o $@
 
+json_help.o : ${R}/common/json_help.c ${R}/common/json_help.h
+	${CROSS_COMPILE}${CC} $(LOCAL_CPPFLAGS) $(PLUGIN_CPPFLAGS) $(PLUGIN_CFLAGS) -c $< -o $@
+
 base_msgs.o : base_msgs.c persist_sqlite.h
 	${CROSS_COMPILE}${CC} $(LOCAL_CPPFLAGS) $(PLUGIN_CPPFLAGS) $(PLUGIN_CFLAGS) -c $< -o $@
 
diff --git a/plugins/persist-sqlite/restore.c b/plugins/persist-sqlite/restore.c
index 03f82ec8..d8fcaefa 100644
--- a/plugins/persist-sqlite/restore.c
+++ b/plugins/persist-sqlite/restore.c
@@ -73,7 +73,7 @@ static mosquitto_property *json_to_properties(const char *json)
 	}
 
 	cJSON_ArrayForEach(obj, array){
-		char *identifier;
+		const char *identifier;
 
 		json_get_string(obj, "identifier", &identifier, true);
 		j_value = cJSON_GetObjectItem(obj, "value");
@@ -164,7 +164,7 @@ static mosquitto_property *json_to_properties(const char *json)
 				break;
 			case MQTT_PROP_TYPE_STRING_PAIR:
 				{
-					char *prop_name;
+					const char *prop_name;
 
 					if(!cJSON_IsString(j_value)){
 						mosquitto_log_printf(MOSQ_LOG_WARNING, "Sqlite persistence: Ignoring %s property whilst restoring, value is incorrect type", "string pair");