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mosquitto-auth-plug

As per 2019-03-11 I am archiving this repository and closing all currently open issues and pull requests without prejudice. The repository will continue to exist and you are welcome to work on your own fork of it, as long as you observe the LICENSEs.

I have not used the mosquitto-auth-plug myself for years now, but my users expect, nay, demand, that I support and help them with it. We've received over 580 stars (thank you for that!), and yet some people can't even be bothered to read the documentation and then send me private e-mails or DMs on Twitter, etc. to complain and/or ask for help. I'm tired of having to work on understanding and fixing issues users are experiencing with the software. I'm also a bit tired of the lack of help I've received for this project.

The original README begins below this line.

mosquitto-auth-plug

This is a plugin to authenticate and authorize Mosquitto users from one or more of a variety of back-ends:

Introduction

This plugin can perform authentication (check username / password) and authorization (grant permission to subscribe and/or publish to specific topics via ACL). Currently, not all back-ends have the same capabilities (see the section on the back-end you're interested in).

Capability cdb files http jwt ldap mongo mysql postgres psk redis sqlite
authentication Y Y Y Y Y Y Y Y Y Y Y
superusers Y Y Y Y Y 3
acl checking 2 Y Y Y Y Y Y 3 1 2
static superusers Y Y Y Y Y Y Y 3 Y Y
  1. Topic wildcards (+/#) are not supported
  2. Currently not implemented; back-end returns TRUE
  3. Dependent on the database used by PSK

Multiple back-ends can be configured simultaneously for authentication, and they're attempted in the order you specify. Once a user has been authenticated, the same back-end is used to check authorization (ACLs). Superusers are checked for in all back-ends. The configuration option is called auth_opt_backends and it takes a comma-separated list of back-end names which are checked in exactly that order.

auth_opt_backends cdb,sqlite,mysql,redis,postgres,http,jwt,mongo

Note: anonymous MQTT connections are assigned a username configured in the plugin as auth_opt_anonusername and they are handled by a so-called fallback back-end which is the first configured back-end.

Passwords are obtained from the back-end as PBKDF2 strings (see Passwords below). If you store a clear-text password or any hash not generated the same way, the comparison and the authentication will fail.

The mysql and mongo back-ends support expansion of %c and %u as clientid and username respectively. This allows ACLs in the database to look like this:

+-----------+---------------------------------+----+
| username  | topic                           | rw |
+-----------+---------------------------------+----+
| bridge-01 | $SYS/broker/connection/%c/state |  2 |
+-----------+---------------------------------+----+

The plugin supports so-called superusers. These are usernames exempt from ACL checking. In other words, if a user is a superuser, that user can access any topic without needing ACLs.

A static superuser is one configured with the fnmatch(3) auth_opt_superusers option. Regular superusers are configured (i.e., enabled) from within the particular database back-end. Effectively, both are identical in that ACL checking is disabled if a user is a superuser.

Note that not all back-ends currently have 'superuser' queries implemented. This is a todo and the auth_opt_superusers option will probably disappear when it is finished.

Building the plugin

In order to compile the plugin you'll require:

  • a copy of the Mosquitto source code together with the libraries required for the back-end you want to use in the plugin, and
  • a recent version of OpenSSL (if the version with your OS, e.g., OS X, is too old, you may need to use one supplied by home brew or build your own).

Copy config.mk.in to config.mk and modify config.mk to suit your building environment. In particular, you have to configure which back-ends you want to provide as well as the path to the Mosquitto source and its library, and possibly the path to OpenSSL (OPENSSLDIR).

After a make you should have a shared object called auth-plug.so which you will reference in your mosquitto.conf.

Configuration

The plugin is configured in Mosquitto's configuration file (typically mosquitto.conf), and it is loaded into Mosquitto auth with the auth_plugin option.

auth_plugin /path/to/auth-plug.so

Options therein with a leading auth_opt_ are handed to the plugin. The following "global" auth_opt_* plugin options exist:

Option default Mandatory Meaning
backends Y comma-separated list of back-ends to load
superusers fnmatch(3) case-sensitive string
log_quiet false don't log DEBUG messages
cacheseconds Deprecated. Alias for acl_cacheseconds
acl_cacheseconds 300 number of seconds to cache ACL lookups. 0 disables
auth_cacheseconds 0 number of seconds to cache AUTH lookups. 0 disables
acl_cachejitter 0 maximum number of seconds to add/remove to ACL lookups cache TTL. 0 disables
auth_cachejitter 0 maximum number of seconds to add/remove to AUTH lookups cache TTL. 0 disables

Individual back-ends each have various additional options described in the sections below.

There are two caches, one for ACL and another for authentication. By default only the ACL cache is enabled.

After a backend responds (postitively or negatively) to an ACL or AUTH lookup, the result will be kept in cache for the configured TTL. The same ACL lookup will be served from the cache as long as the TTL is valid. The configured TTL is the auth_cacheseconds/acl_cacheseconds combined with a random value between -auth_/acl_cachejitter and +auth_/acl_cachejitter. For example, with an acl_cacheseconds of 300 and acl_cachejitter of 10, ACL lookup TTLs are distributed between 290 and 310 seconds.

Set auth/acl_cachejitter to 0 disable any randomization of cache TTL. Setting auth/acl_cacheseconds to 0 disables caching entirely. Caching is useful when your backend lookup is expensive. Remember that ACL lookup will be performed for each message which is sent/received on a topic. Jitter is useful to reduce lookup storms that could occur every auth/acl_cacheseconds if lots of clients connect at the same time (for example, after a server restart, all your clients may reconnect immediately and each cause ACL lookups every acl_cacheseconds).

MySQL auth

The mysql back-end is currently the most feature-complete: it supports obtaining passwords, checking for superusers, and verifying ACLs by configuring up to three distinct SQL queries used to obtain those results.

You configure the SQL queries in order to adapt to whichever schema you currently have.

The following auth_opt_ options are supported by the mysql back-end:

Option default Mandatory Meaning
host localhost hostname/address
port 3306 TCP port
user username
pass password
dbname Y database name
userquery Y SQL for users
superquery SQL for superusers
aclquery SQL for ACLs
mysql_opt_reconnect true enable MYSQL_OPT_RECONNECT option
mysql_auto_connect true enable auto_connect function
anonusername anonymous username to use for anonymous connections
ssl_enabled false enable SSL
ssl_key path name of client private key file
ssl_cert path name of client public key certificate file
ssl_ca path name of Certificate Authority(CA) certificate file
ssl_capath path name of directory that contains trusted CA certifcate files
ssl_cipher permitted ciphers for SSL encryption

The SQL query for looking up a user's password hash is mandatory. The query MUST return a single row only (any other number of rows is considered to be "user not found"), and it MUST return a single column with only the PBKDF2 password hash. Two '%s' in the auth_opt_userquery string are replaced by the username attempting to access the broker and the clientid, in that order. If the clientid is not to be used in the SQL, insert just a single '%s':

SELECT pw FROM users WHERE username = '%s' LIMIT 1

The SQL query for checking whether a user is a superuser - and thus circumventing ACL checks - is optional. If it is specified, the query MUST return a single row with a single value: 0 is false and 1 is true. We recommend using a SELECT IFNULL(COUNT(*),0) FROM ... for this query as it satisfies both conditions. A single '%s' in the auth_opt_superquery string is replaced by the username attempting to access the broker. The following example uses the same users table, but it could just as well reference a distinct table or view.

SELECT IFNULL(COUNT(*), 0) FROM users WHERE username = '%s' AND super = 1

The SQL query for checking ACLs is optional, but if it is specified, the mysql back-end can try to limit access to particular topics or topic branches depending on the value of a database table. The query MAY return zero or more rows for a particular user, each containing EXACTLY one column containing a topic (wildcards are supported). A single '%s' in the query string is replaced by the username attempting to access the broker, and a single '%d' is replaced with an integer, 1 signifying a read-only access attempt (SUB) or 2 signifying a read-write access attempt (PUB).

In the following example, the table has an INT(1) column rw containing 1 for readonly topics, and 2 for read-write topics:

SELECT topic FROM acls WHERE (username = '%s') AND (rw >= %d)

Sample Mosquitto configuration (e.g., mosquitto.conf) for the mysql back-end:

auth_plugin /home/jpm/mosquitto-auth-plug/auth-plug.so
auth_opt_host localhost
auth_opt_port 3306
auth_opt_dbname test
auth_opt_user jjj
auth_opt_pass supersecret
auth_opt_userquery SELECT pw FROM users WHERE username = '%s'
# auth_opt_userquery SELECT pwhash FROM user WHERE username = '%s' AND clientid = '%s'
auth_opt_superquery SELECT COUNT(*) FROM users WHERE username = '%s' AND super = 1
auth_opt_aclquery SELECT topic FROM acls WHERE (username = '%s') AND (rw >= %d)
auth_opt_anonusername AnonymouS

Assuming the following database tables:

mysql> SELECT * FROM users;
+----+----------+---------------------------------------------------------------------+-------+
| id | username | pw                                                                  | super |
+----+----------+---------------------------------------------------------------------+-------+
|  1 | jjolie   | PBKDF2$sha256$901$x8mf3JIFTUFU9C23$Mid2xcgTrKBfBdye6W/4hE3GKeksu00+ |     0 |
|  2 | a        | PBKDF2$sha256$901$XPkOwNbd05p5XsUn$1uPtR6hMKBedWE44nqdVg+2NPKvyGst8 |     0 |
|  3 | su1      | PBKDF2$sha256$901$chEZ4HcSmKtlV0kf$yRh2N62uq6cHoAB6FIrxIN2iihYqNIJp |     1 |
+----+----------+---------------------------------------------------------------------+-------+

mysql> SELECT * FROM acls;
+----+----------+-------------------+----+
| id | username | topic             | rw |
+----+----------+-------------------+----+
|  1 | jjolie   | loc/jjolie        |  1 |
|  2 | jjolie   | $SYS/something    |  1 |
|  3 | a        | loc/test/#        |  1 |
|  4 | a        | $SYS/broker/log/+ |  1 |
|  5 | su1      | mega/secret       |  1 |
|  6 | nop      | mega/secret       |  1 |
+----+----------+-------------------+----+

the above SQL queries would enable the following combinations (the * at the beginning of the line indicates a superuser)

  jjolie     PBKDF2$sha256$901$x8mf3JIFTUFU9C23$Mid2xcgTrKBfBdye6W/4hE3GKeksu00+
	loc/a                                    DENY
	loc/jjolie                               PERMIT
	mega/secret                              DENY
	loc/test                                 DENY
	$SYS/broker/log/N                        DENY
  nop        <nil>
	loc/a                                    DENY
	loc/jjolie                               DENY
	mega/secret                              PERMIT
	loc/test                                 DENY
	$SYS/broker/log/N                        DENY
  a          PBKDF2$sha256$901$XPkOwNbd05p5XsUn$1uPtR6hMKBedWE44nqdVg+2NPKvyGst8
	loc/a                                    DENY
	loc/jjolie                               DENY
	mega/secret                              DENY
	loc/test                                 PERMIT
	$SYS/broker/log/N                        PERMIT
* su1        PBKDF2$sha256$901$chEZ4HcSmKtlV0kf$yRh2N62uq6cHoAB6FIrxIN2iihYqNIJp
	loc/a                                    PERMIT
	loc/jjolie                               PERMIT
	mega/secret                              PERMIT
	loc/test                                 PERMIT
	$SYS/broker/log/N                        PERMIT

The mysql back-end will re-connect to the MySQL server when the connection has been lost. If you wish, you can disable this by configuring:

auth_opt_mysql_opt_reconnect false
auth_opt_mysql_auto_connect false

LDAP auth

The LDAP plugin currently does authentication only; authenticated users are allowed to publish/subscribe at will.

The user that connects to the broker is searched for in the LDAP directory indicated via the ldap_uri configuration parameter. This LDAP search MUST return exactly one entry. The user's password is then used with the DN of the that entry to bind to the directory. If that LDAP bind succeeds, the user is authenticated. In all other cases, authentication fails.

Option default Mandatory Meaning
binddn Y the DN of an object which may search users
bindpw Y its password
ldap_uri Y an LDAP uri with filter
ldap_acl_deny false return DENY instead of ALLOW to ACL checks

Example configuration:

auth_plugin /path/to/auth-plug.so
auth_opt_backends ldap
auth_opt_binddn cn=manager,dc=mens,dc=de
auth_opt_bindpw s3crit
auth_opt_ldap_uri ldap://127.0.0.1/ou=Users,dc=mens,dc=de?cn?sub?(&(objectclass=inetOrgPerson)(uid=@))
auth_opt_ldap_acl_deny false

With the ldap_acl_deny we return DENY instead of ALLOW for every ACL check. This makes it possible to chain other backends with ldap backend, and use LDAP for authentification and, e.g., MySQL for ACL checking.

CDB auth

Option default Mandatory Meaning
cdbname Y path to .cdb

SQLITE auth

Option default Mandatory Meaning
dbpath Y path to database
sqliteuserquery Y SQL for users

Example:

auth_opt_sqliteuserquery SELECT pw FROM users WHERE username = ?

Redis auth

auth_opt_redis_userquery GET %s
auth_opt_redis_aclquery GET %s-%s

In auth_opt_redis_userquery the %s parameter is the username, whereas in auth_opt_redis_aclquery, the first %s is the username and the second is the topic. When using ACLs, topic must be an exact match - wildcards are not supported.

If no options are provided, then the plugin will default to not using an ACL and using the above userquery.

Option default Mandatory Meaning
redis_host localhost hostname / IP address
redis_port 6379 TCP port number

HTTP auth

The http back-end is for auth by custom HTTP API.

The following auth_opt_ options are supported by the http back-end:

Option default Mandatory Meaning
http_ip Y IP address, will skip DNS lookup
http_port 80 TCP port number
http_hostname hostname for HTTP header
http_getuser_uri Y URI for checking username/password
http_superuser_uri Y URI for checking superuser
http_aclcheck_uri Y URI for checking acl
http_with_tls false Use TLS on connect
http_basic_auth_key Basic Authentication Key
http_retry_count 3 Number of retries done if backend is unavailable

If the configured URLs return an HTTP status code == 2xx, the authentication / authorization succeeds. If the status code == 4xx, authentication / authorization fails. For a status code == 5xx or server Unreachable, the HTTP request will be retried up to http_retry_count. If all tries fail and if no other backend succeeded, then an error is returned and the client is disconnected.

URI-Param username password clientid topic acc
http_getuser_uri Y Y N N N
http_superuser_uri Y N N N N
http_aclcheck_uri Y N Y Y Y

Mosquitto configuration for the http back-end:

auth_opt_backends http
auth_opt_http_ip 127.0.0.1
auth_opt_http_port 8089
#auth_opt_http_hostname example.org
auth_opt_http_getuser_uri /auth
auth_opt_http_superuser_uri /superuser
auth_opt_http_aclcheck_uri /acl

A very simple example service using Python and bottle can be found in examples/http-auth-be.py.

The http plugin can utilize environment variables which are exported before it (i.e., Mosquitto) is started by adding configuration settings like

auth_opt_<interface>_<method>_params <key>=<evn_name>[,<key>=<evn_name>]*

For example, set the following:

export DOMAIN=example.com
export PORT=8080

and add the following settings to mosquitto.conf:

auth_opt_http_getuser_params domain=DOMAIN,port=PORT
auth_opt_http_superuser_params domain=DOMAIN,port=PORT
auth_opt_http_aclcheck_params domain=DOMAIN,port=PORT

JWT auth

The jwt back-end is for auth by JWT-webtokens. The JWT and HTTP configurations are identical, so please read the http-section above.

The username field is interpreted as the token-field and passed to the http-server in an Authorization-header.

Authorization: Bearer %token

Note: Some clients require the password field to be populated. This field is ignored by the JWT-backend, so feel free to input some gibberish.

PostgreSQL auth

The postgres back-end, like mysql, is currently the most feature-complete: it supports distinct SQL queries for obtaining passwords, checking for superusers, and verifying ACLs, each configurable to suit your schema.

The following auth_opt_ options are supported by the postgres back-end:

Option default Mandatory Meaning
host localhost hostname/address
port 5432 TCP port
user username
pass password
dbname Y database name
userquery Y SQL for users
superquery SQL for superusers
aclquery SQL for ACLs
sslcert SSL/TLS Client Cert.
sslkey SSL/TLS Client Cert. Key

The SQL query for looking up a user's password hash is mandatory. The query must return a single row only (any other number of rows is considered to be "user not found"), and it must return a single column only with the PBKDF2 password hash. A single $1 in the query string is replaced by the username attempting to access the broker.

SELECT pass FROM account WHERE username = $1 limit 1

The SQL query for checking whether a user is a superuser - and thus circumventing ACL checks - is optional. If it is specified, the query must return a single row with a single value: 0 is false and 1 is true. We recommend using a SELECT COALESCE(COUNT(*),0) FROM ... for this query as it satisfies both conditions. A single $1 in the auth_opt_superquery string is replaced by the username attempting to access the broker. The following example uses the same account table, but it could just as well reference a distinct table or view.

SELECT COALESCE(COUNT(*),0) FROM account WHERE username = $1 AND super = 1

The SQL query for checking ACLs is optional, but if it is specified, the postgres back-end can try to limit access to particular topics or topic branches depending on the value of a database table. The query MAY return zero or more rows for a particular user, each containing EXACTLY one column containing a topic (wildcards are supported). A single $1 in the query string is replaced by the username attempting to access the broker, and a single $2 is replaced with an integer, 1 signifying a read-only access attempt (SUB) or 2 signifying a read-write access attempt (PUB).

In the following example, the table has a column rw containing 1 for readonly topics, 2 for writeonly topics and 3 for readwrite topics:

SELECT topic FROM acl WHERE (username = $1) AND rw >= $2

Sample Mosquitto configuration for the postgres back-end:

auth_plugin /home/jpm/mosquitto-auth-plug/auth-plug.so
auth_opt_host localhost
auth_opt_port 5432
auth_opt_dbname test
auth_opt_user jjj
auth_opt_pass supersecret
auth_opt_userquery SELECT pw FROM account WHERE username = $1 limit 1
auth_opt_superquery SELECT COALESCE(COUNT(*),0) FROM account WHERE username = $1 AND mosquitto_super = 1
auth_opt_aclquery SELECT topic FROM acls WHERE (username = $1) AND (rw & $2) > 0
auth_opt_sslcert /etc/postgresql/ssl/client.crt
auth_opt_sslkey /etc/postgresql/ssl/client.key

Assuming the following database tables:

=> SELECT * FROM account;
+----+----------+---------------------------------------------------------------------+-------+
| id | username | pw                                                                  | super |
+----+----------+---------------------------------------------------------------------+-------+
|  1 | jjolie   | PBKDF2$sha256$901$x8mf3JIFTUFU9C23$Mid2xcgTrKBfBdye6W/4hE3GKeksu00+ |     0 |
|  2 | a        | PBKDF2$sha256$901$XPkOwNbd05p5XsUn$1uPtR6hMKBedWE44nqdVg+2NPKvyGst8 |     0 |
|  3 | su1      | PBKDF2$sha256$901$chEZ4HcSmKtlV0kf$yRh2N62uq6cHoAB6FIrxIN2iihYqNIJp |     1 |
+----+----------+---------------------------------------------------------------------+-------+

=> SELECT * FROM acls;
+----+----------+-------------------+----+
| id | username | topic             | rw |
+----+----------+-------------------+----+
|  1 | jjolie   | loc/jjolie        |  1 |
|  2 | jjolie   | $SYS/something    |  1 |
|  3 | a        | loc/test/#        |  1 |
|  4 | a        | $SYS/broker/log/+ |  1 |
|  5 | su1      | mega/secret       |  1 |
|  6 | nop      | mega/secret       |  1 |
+----+----------+-------------------+----+

the above SQL queries would enable the following combinations (the * at the beginning of the line indicates a superuser)

  jjolie     PBKDF2$sha256$901$x8mf3JIFTUFU9C23$Mid2xcgTrKBfBdye6W/4hE3GKeksu00+
  loc/a                                    DENY
  loc/jjolie                               PERMIT
  mega/secret                              DENY
  loc/test                                 DENY
  $SYS/broker/log/N                        DENY
  nop        <nil>
  loc/a                                    DENY
  loc/jjolie                               DENY
  mega/secret                              PERMIT
  loc/test                                 DENY
  $SYS/broker/log/N                        DENY
  a          PBKDF2$sha256$901$XPkOwNbd05p5XsUn$1uPtR6hMKBedWE44nqdVg+2NPKvyGst8
  loc/a                                    DENY
  loc/jjolie                               DENY
  mega/secret                              DENY
  loc/test                                 PERMIT
  $SYS/broker/log/N                        PERMIT
* su1        PBKDF2$sha256$901$chEZ4HcSmKtlV0kf$yRh2N62uq6cHoAB6FIrxIN2iihYqNIJp
  loc/a                                    PERMIT
  loc/jjolie                               PERMIT
  mega/secret                              PERMIT
  loc/test                                 PERMIT
  $SYS/broker/log/N                        PERMIT

Note that the above sample auth_opt_aclquery is sensitive to new permission values used in Mosquitto 1.5.

You can either adapt to the updated binary-style permissions (2 for write, 5 for read+subscribe, 7 for read/write), modify your query to work around them, or modify the constants in the Mosquitto source.

MongoDB auth

The mongo back-end works with superuser and ACL checks. Additional build dependencies are https://github.com/mongodb/mongo-c-driver >=1.4.0 and https://github.com/mongodb/libbson >=1.4.0.

You should set up a users collection (required) and a topic lists collection (optional) with the following format:

Users collection

Each user document must have a username, a hashed password, and at least one of:

  • A superuser prop, allowing full access to all topics
  • An embedded array or sub-document to use as an ACL (see 'ACL format')
  • A foreign key pointing to another document containing an ACL (see 'ACL format')

You may use any combination of these options; authorisation will be granted if any check passes.

The user document has the following format (note that the property names are configurable variables, see 'Configuration').

{
    [user_username_prop]: string, // Username as given in the MQTT connect request
    [user_password_prop]: string, // A PBKDF2 hash, see 'Passwords' section
    [user_topiclist_fk_prop]: int | oid | string, // reference to a document in collection_topics)
    [user_topics_prop]: string[] | { [topic: string]: "r"|"w"|"rw" }, // see 'ACL format'
    [user_superuser_prop]: int | boolean // optional, superuser if truthy
}

As an example using default options, a user document with an embedded ACL might look like:

{
    "username": "user1",
    "password": "PBKDF2$sha256$901$8ebTR72Pcmjl3cYq$SCVHHfqn9t6Ev9sE6RMTeF3pawvtGqTu",
    "superuser": false,
    "topics": {
        "public/#": "r",
	"client/user1/#": "rw"
    }
}

Topic lists collection (optional)

If the user document references a separate topics document, that document should exist and must have the format:

{
    [topiclist_key_prop]: int | oid | string, // unique id, as referenced by users[user_topiclist_fk_prop],
    [topiclist_topics_prop]: string[] | { [topic: string]: "r"|"w"|"rw" } // see 'ACL format'
}

This strategy will be especially suitable if you have a complex ACL shared between many users.

ACL format

Topics may be given as either an array of topic strings, eg ["topic1/#", "topic2/+"], in which case all topics will be read-write, or as a sub-document mapping topic names to the strings "r", "w", "rw", eg { "article/#":"r", "article/+/comments":"rw", "ballotbox":"w" }.

Configuration

The following auth_opt_mongo_ options are supported by the mongo back-end:

Option default Meaning
uri mongodb://localhost:27107 MongoDB connection string (database part is ignored)
database mqGate Name of the database containing users (and topiclists)
user_coll users Collection for user documents
topiclist_coll topics Collection for topiclist documents (optional if embedded topics are used)
user_username_prop username Username property name in the user document
user_password_prop password Password property name in the user document
user_superuser_prop superuser Superuser property name in the user document
user_topics_prop topics Name of a property on the user document containing an embedded topic list
user_topiclist_fk_prop topics Property used as a foreign key to reference a topiclist document
topiclist_key_prop _id Unique key in the topiclist document pointed to by user_topiclist_fk_prop
topiclist_topics_prop topics Property containing topics within the topiclist document

Mosquitto configuration for the mongo back-end:

auth_plugin /home/jpm/mosquitto-auth-plug/auth-plug.so
auth_opt_mongo_uri mongodb://localhost:27017

Files auth

The files backend attempts to re-implement the files behavior in vanilla Mosquitto, however the user's password file contains PBKDF2 passwords instead of passwords hashed with the mosquitto-passwd program; you would use our np utility or similar to create the PBKDF2 hashes.

The configuration directives for the Files backend are as follows:

auth_opt_backends files
auth_opt_password_file file.pw
auth_opt_acl_file file.acl

with examples of these files being:

password_file

# comment
jpm:PBKDF2$sha256$901$UGfDz79cAaydRsEF$XvYwauPeviFd1NfbGL+dxcn1K7BVfMeW
jane:PBKDF2$sha256$901$wvvH0fe7Ftszt8nR$NZV6XWWg01dCRiPOheVNsgMJDX1mzd2v

acl_file

user jane
topic read #

user jpm
topic dd

The syntax for the ACL file is that as described in mosquitto.conf(5).

PSK auth

If Mosquitto has been built with PSK support, and auth-plug has been built with BE_PSK defined, it supports authenticating PSK connections over TLS, as long as Mosquitto is appropriately configured.

The way this works is that the psk back-end actually uses one of auth-plug's other databases (mysql, sqlite, cdb, etc.) to obtain the pre-shared key from the "users" query, and it uses the same database's back-end for performing authorization (aka ACL checks).

Consider the following mosquitto.conf snippet:

...
auth_opt_psk_database mysql
...
listener 8885
psk_hint hint1
tls_version tlsv1
use_identity_as_username true

TLS PSK is available on port 8885 and is activated with, say,

mosquitto_pub -h localhost -p 8885 -t x -m hi --psk-identity ps2 --psk 020202

The use_identity_as_username option has auth-plug see the name ps2 as the username, and this is given to the database back-end (here: mysql) to look up the password as defined for the mysql back-end. auth-plug uses its getuser() query to read the clear-text (not PKBDF2) hex key string which it returns to Mosquitto for authentication. If authentication passes, the connection is established.

For authorization, auth_plug uses the identity as the username and the topic to perform ACL-checking as described earlier.

The following log-snippet serves as an illustration:

New connection from ::1 on port 8885.
|-- psk_key_get(hint1, ps1) from [mysql] finds PSK: 1
New client connected from ::1 as mosqpub/90759-tiggr.ww. (c1, k60).
Sending CONNACK to mosqpub/90759-tiggr.ww. (0)
|-- user ps1 was authenticated in back-end 0 (psk)
|--   mysql: topic_matches(x, x) == 1
|-- aclcheck(ps1, x, 2) AUTHORIZED=1 by psk
Received PUBLISH from mosqpub/90759-tiggr.ww. (d0, q0, r0, m0, 'x', ... (2 bytes))
Received DISCONNECT from mosqpub/90759-tiggr.ww.

In the case of this MySQL example, we added the clear text of the PSK key to the database:

mysql> INSERT INTO user (username, pwhash, superuser) VALUES ('mylistener', 'F0BEEF', 0);

Passwords

A user's password is stored as a PBKDF2 hash in the back-end. An example "password" is a string with five pieces in it, delimited by $, inspired by this.

PBKDF2$sha256$901$8ebTR72Pcmjl3cYq$SCVHHfqn9t6Ev9sE6RMTeF3pawvtGqTu
--^--- --^--- -^- ------^--------- -------------^------------------
  |      |     |        |                       |
  |      |     |        |                       +-- : hashed password
  |      |     |        +-------------------------- : salt
  |      |     +----------------------------------- : iterations
  |      +----------------------------------------- : hash function
  +------------------------------------------------ : marker

Note that the salt by default will be taken as-is (thus it will not be base64 decoded before the validation). In case your own implementation uses the raw bytes when hashing the password and base64 is only used for display purpose, compile this project with the -DRAW_SALT flag (you could add this in the config.mk file to CFG_CFLAGS).

Creating a user

A trivial utility to generate hashes is included as np. Copy and paste the whole string generated into the respective back-end.

$ np
Enter password:
Re-enter same password:
PBKDF2$sha256$901$Qh18ysY4wstXoHhk$g8d2aDzbz3rYztvJiO3dsV698jzECxSg

For example, in Redis:

$ redis-cli
> SET n2 PBKDF2$sha256$901$Qh18ysY4wstXoHhk$g8d2aDzbz3rYztvJiO3dsV698jzECxSg
> QUIT

Configuring Mosquitto

listener 1883

auth_plugin /path/to/auth-plug.so
auth_opt_redis_host 127.0.0.1
auth_opt_redis_port 6379

# Usernames with this fnmatch(3) (a.k.a glob(3))  pattern are exempt from the
# module's ACL checking
auth_opt_superusers S*

ACL

In addition to the ACL checking which might be performed by a back-end, there's a more "static" checking which can be configured in mosquitto.conf.

Note that if ACLs are being verified by the plugin, this also applies to Will topics (last will and testament). Failing to correctly set up an ACL for these, will cause a broker to silently fail with a 'not authorized' message.

Users can be given "superuser" status (i.e. they may access any topic) if their username matches the glob specified in auth_opt_superusers.

In our example above, any user with a username beginning with a capital "S" is exempt from ACL-checking.

PUB/SUB

At this point you ought to be able to connect to Mosquitto using, e.g., the Mosquitto client:

mosquitto_pub  -t '/location/n2' -m hello -u n2 -P secret

Requirements

  • A Mosquitto broker
  • OpenSSL (tested with 1.0.0c, but should work with earlier versions)

Some of the back-ends require a server instance or client libraries. For example:

  • for redis: a Redis server and hiredis, the Minimalistic C client for Redis
  • for cdb: TinyCDB by Michael Tokarev (included in contrib/)
  • for postgres: the latest dev version of postgresql-server

Credits

  • Uses base64.[ch] (and yes, I know OpenSSL has base64 routines, but no thanks). These files are

Copyright (c) 1995, 1996, 1997 Kungliga Tekniska Hgskolan (Royal Institute of Technology, Stockholm, Sweden).

  • Uses uthash by Troy D. Hanson.

Possibly related

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