Auth using a database

VerneMQ supports multiple ways to authenticate and authorize new client connections using a database.

Introduction and general setup

VerneMQ supports authentication and authorization using a number of popular databases and the below sections describe how to configure the different databases.

The database drivers are handled using the vmq_diversity plugin and it therefore needs to be enabled:

plugins.vmq_diversity = on

The vmq_diversity plugin makes it possible to extend VerneMQ using Lua. The documentation can be found here.

When using database based authentication/authorization the enabled-by-default file based authentication and authorization are most likely not needed and should be disabled:

plugins.vmq_passwd = off
plugins.vmq_acl = off

You must set allow_anonymous = off, otherwise VerneMQ won't use the database plugin for authentication and authorization.

In order to use a database for authentication and authorization the database must be properly configured and the auth-data (username, clientid, password, acls) to be present. The following sections show some sample requests that can be used to insert such data.

While the handling of authentication differs among the different databases, the handling of ACLs is roughly identical and make use of a JSON array containing one or many ACL objects per configured client.

The database integrations will cache the ACLs when the client connects avoiding expensive database lookups for each publish or subscribe message. The cache entries are evicted when the client disconnects.

A minimal publish & subscribe ACL JSON object takes the following form:

General ACL

{
    "pattern": "a/+/c"
}

The pattern is a MQTT topic string that can contain MQTT wildcards, but also the template variables %m (mountpoint), %u (username), and %c (client id) which are automatically substituted with the auth data provided.

Publish ACL

The publish ACL makes it possible to control the maximum QoS and payload size that is allowed, and if the message is allowed to be retained.

{
    "pattern": "a/+/c",
    "max_qos": 2,
    "max_payload_size": 128,
    "allowed_retain": true
}

Moreover, the publish ACL makes it possible to modify the properties of a published message through specifying one or multiple modifiers. Please note that the modified message isn't re-validated by the ACL.

{
    "pattern": "a/+/c",
    "max_qos": 2,
    "max_payload_size": 128,
    "allowed_retain": true,
    "modifiers": {
        "topic": "new/topic",
        "payload": "new payload",
        "qos": 2,
        "retain": true,
        "mountpoint": "other-mountpoint"
    }
}

Subscribe ACL

The subscribe ACL makes it possible to control the maxium QoS a client is allowed to subscribe to.

{
    "pattern": "a/+/c",
    "max_qos": 2
}

Like the publish ACL, the subscribe ACL makes it possible to change the current subscription request by returning a custom set of topic/qos pairs. Please note that the modified subscription isn't re-validated by the ACL.

{
    "pattern": "a/+/c",
    "max_qos": 2,
    "modifiers": [
        ["new/topic/1", 1],
        ["new/topic/2", 1]
    ]
}

Password verification and hashing methods

When deciding on which database to use one has to consider which kind of password hashing and key derivation functions are available and required. Different databases provide different mechanisms, for example PostgreSQL provides the pgcrypto module which supports verifying hashed and salted passwords, while Redis has no such features. VerneMQ therefore also provides client-side password verification mechanisms such as bcrypt.

There is a trade-off between verifying passwords on the client-side versus on the server-side. Verifying passwords client-side of course means doing the computations on the VerneMQ broker and this takes away resources from other tasks such as routing messages. With hashing functions such as bcrypt which are designed specifically to be slow (proportional to the number of rounds) in order to make brute-force attacks infeasible, this can become a problem. For example, if verifying a password with bcrypt takes 0.5 seconds then on a single threaded core 2 verifications/second are possible and using 4 single threaded cores 8 verifications/second. So, the number of rounds/security paramenters have a direct impact on the max number of verifications/second and hence also the maximum arrival rate of new clients per second.

For each database it is specified which password verification mechanisms are available and if they are client-side or server-side.

PostgreSQL

To enable PostgreSQL authentication and authorization the following need to be configured in the vernemq.conf file:

vmq_diversity.auth_postgres.enabled = on
vmq_diversity.postgres.host = 127.0.0.1
vmq_diversity.postgres.port = 5432
vmq_diversity.postgres.user = vernemq
vmq_diversity.postgres.password = vernemq
vmq_diversity.postgres.database = vernemq_db
vmq_diversity.postgres.password_hash_method = crypt

PostgreSQL hashing methods:

method	client-side	server-side
bcrypt	✓
crypt		✓

The following SQL DDL must be applied, the pgcrypto extension is required if using the server-side crypt hashing method:

CREATE EXTENSION pgcrypto;
CREATE TABLE vmq_auth_acl
 (
   mountpoint character varying(10) NOT NULL,
   client_id character varying(128) NOT NULL,
   username character varying(128) NOT NULL,
   password character varying(128),
   publish_acl json,
   subscribe_acl json,
   CONSTRAINT vmq_auth_acl_primary_key PRIMARY KEY (mountpoint, client_id, username)
 );

To enter new ACL entries use a query similar to the following:

WITH x AS (
    SELECT
        ''::text AS mountpoint,
           'test-client'::text AS client_id,
           'test-user'::text AS username,
           '123'::text AS password,
           gen_salt('bf')::text AS salt,
           '[{"pattern": "a/b/c"}, {"pattern": "c/b/#"}]'::json AS publish_acl,
           '[{"pattern": "a/b/c"}, {"pattern": "c/b/#"}]'::json AS subscribe_acl
    ) 
INSERT INTO vmq_auth_acl (mountpoint, client_id, username, password, publish_acl, subscribe_acl)
    SELECT 
        x.mountpoint,
        x.client_id,
        x.username,
        crypt(x.password, x.salt),
        publish_acl,
        subscribe_acl
    FROM x;

CockroachDB

To enable PostgreSQL authentication and authorization the following need to be configured in the vernemq.conf file:

vmq_diversity.auth_cockroachdb.enabled = on
vmq_diversity.cockroachdb.host = 127.0.0.1
vmq_diversity.cockroachdb.port = 26257
vmq_diversity.cockroachdb.user = vernemq
vmq_diversity.cockroachdb.password = vernemq
vmq_diversity.cockroachdb.database = vernemq_db
vmq_diversity.cockroachdb.ssl = on
vmq_diversity.cockroachdb.password_hash_method = bcrypt

Notice that if the CockroachDB installation is secure, then TLS is required. If using an insecure installation without TLS, then vmq_diversity.cockroachdb.ssl can be set to off.

CockroachDB hashing methods:

method	client-side	server-side
bcrypt	✓
sha256		✓

The following SQL DDL must be applied:

CREATE TABLE vmq_auth_acl
 (
   mountpoint character varying(10) NOT NULL,
   client_id character varying(128) NOT NULL,
   username character varying(128) NOT NULL,
   password character varying(128),
   publish_acl json,
   subscribe_acl json,
   CONSTRAINT vmq_auth_acl_primary_key PRIMARY KEY (mountpoint, client_id, username)
 );

To enter new ACL entries use a query similar to the following, the example is for the bcrypt hashing method:

WITH x AS (
    SELECT
        ''::text AS mountpoint,
           'test-client1'::text AS client_id,
           'test-user1'::text AS username,
           '$2a$12$97PlnSsouvCV7HaxDPV80.EXfsKM4Fg7DAwWhSbGJ6O5CpNep20n2'::text AS hash,
           '[{"pattern": "a/b/c"}, {"pattern": "c/b/#"}]'::json AS publish_acl,
           '[{"pattern": "a/b/c"}, {"pattern": "c/b/#"}]'::json AS subscribe_acl
    )
INSERT INTO vmq_auth_acl (mountpoint, client_id, username, password, publish_acl, subscribe_acl)
    SELECT
        x.mountpoint,
        x.client_id,
        x.username,
        x.hash,
        publish_acl,
        subscribe_acl
    FROM x;

MySQL

For MySQL authentication and authorization configure the following in vernemq.conf:

vmq_diversity.auth_mysql.enabled = on
vmq_diversity.mysql.host = 127.0.0.1
vmq_diversity.mysql.port = 3306
vmq_diversity.mysql.user = vernemq
vmq_diversity.mysql.password = vernemq
vmq_diversity.mysql.database = vernemq_db
vmq_diversity.mysql.password_hash_method = password

MySQL hashing methods:

method	client-side	server-side
sha256		✓
md5*		✓
sha1*		✓
password		✓

It should be noted that all the above options stores unsalted passwords which are vulnerable to rainbow table attacks, so the threat-model should be considered carefully when using these. Also note the methods marked with * are no longer considered secure hashes.

The following SQL DDL must be applied:

CREATE TABLE vmq_auth_acl
(
  mountpoint VARCHAR(10) NOT NULL,
  client_id VARCHAR(128) NOT NULL,
  username VARCHAR(128) NOT NULL,
  password VARCHAR(128),
  publish_acl TEXT,
  subscribe_acl TEXT,
  CONSTRAINT vmq_auth_acl_primary_key PRIMARY KEY (mountpoint, client_id, username)
)

To enter new ACL entries use a query similar to the following, the example uses PASSWWORD to for password hashing:

INSERT INTO vmq_auth_acl 
    (mountpoint, client_id, username, 
     password, publish_acl, subscribe_acl)
VALUES 
    ('', 'test-client', 'test-user', PASSWORD('123'), 
     '[{"pattern":"a/b/c"},{"pattern":"c/b/#"}]', 
     '[{"pattern":"a/b/c"},{"pattern":"c/b/#"}]');

Note, the PASSWORD() hashing method needs to be changed according to the configuration set in vmq_diversity.mysql.password_hash_method, it supports the options password, md5, sha1 and sha256. Learn more about the MySQL equivalent for those methods on https://dev.mysql.com/doc/refman/8.0/en/encryption-functions.html.

The default password method has been deprecated since MySQL 5.7.6 and not usable with MySQL 8.0.11+. Also, the MySQL authentication method caching_sha2_password is not supported. This is the default in MySQL 8.0.4 and later, so you need to add: default_authentication_plugin=mysql_native_password under [mysqld] in e.g. /etc/mysql/my.cnf.

MongoDB

For MongoDB authentication and authorization configure the following in vernemq.conf:

vmq_diversity.auth_mongodb.enabled = on
vmq_diversity.mongodb.host = 127.0.0.1
vmq_diversity.mongodb.port = 27017
# vmq_diversity.mongodb.login =
# vmq_diversity.mongodb.password = 
# vmq_diversity.mongodb.database =

MongoDB hashing methods:

method	client-side	server-side
bcrypt	✓

Insert the ACL using the mongo shell or any software library. The passhash property contains the bcrypt hash of the clients password.

db.vmq_acl_auth.insert({
    mountpoint: '', 
    client_id: 'test-client', 
    username: 'test-user', 
    passhash: '$2a$12$WDzmynWSMRVzfszQkB2MsOWYQK9qGtfjVpO8iBdimTOjCK/u6CzJK', 
    publish_acl: [
        {pattern: 'a/b/c'}, 
        {pattern: 'a/+/d'}
    ], 
    subscribe_acl: [
        {pattern: 'a/#'}
    ]
})

Redis

For Redis authentication and authorization configure the following in vernemq.conf:

vmq_diversity.auth_redis.enabled = on
vmq_diversity.redis.host = 127.0.0.1
vmq_diversity.redis.port = 6379
# vmq_diversity.redis.password = 
# vmq_divserity.redis.database = 0

Redis hashing methods:

method	client-side	server-side
bcrypt	✓

Insert the ACL using the redis-cli shell or any software library. The passhash property contains the bcrypt hash of the clients password. The key is an encoded JSON array containing the mountpoint, username, and client id. Note that no spaces are allowed between the array items.

SET "[\"\",\"test-client\",\"test-user\"]" "{\"passhash\":\"$2a$12$WDzmynWSMRVzfszQkB2MsOWYQK9qGtfjVpO8iBdimTOjCK/u6CzJK\",\"subscribe_acl\":[{\"pattern\":\"a/+/c\"}]}"

Note, currently bcrypt version 2a (prefix $2a$) is supported.