.. _kafka_sasl_auth:

Authentication with SASL
-------------------------

**Table of Contents**

.. contents::
  :local:
  :depth: 1


SASL Overview
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Kafka brokers supports client authentication via SASL. SASL authentication can be enabled concurrently with SSL encryption (SSL client authentication will be disabled).

The supported SASL mechanisms are:

* GSSAPI (Kerberos)
* SCRAM
* PLAIN

GSSAPI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. toctree::
   :maxdepth: 1

   authentication_sasl_gssapi

SCRAM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. toctree::
   :maxdepth: 1

   authentication_sasl_scram

PLAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. toctree::
   :maxdepth: 1

   authentication_sasl_plain


JAAS configurations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As part of enabling any of the SASL authentication mechanisms, you must provide Java Authentication and Authorization Service (JAAS) configurations.

Brokers can configure JAAS by passing a static JAAS configuration file into the JVM using the ``java.security.auth.login.config`` property at runtime. For example:

.. sourcecode:: bash

   $ export KAFKA_OPTS="-Djava.security.auth.login.config=/etc/kafka/kafka_server_jaas.conf"
   $ bin/kafka-server-start etc/kafka/server.properties

Clients, on the other hand, have two ways to configure JAAS:

1. pass a static JAAS configuration file into the JVM using the ``java.security.auth.login.config`` property at runtime, as done with brokers
2. embed the JAAS configuration itself in the configuration property ``sasl.jaas.config``

The preferred method for clients is the second way: to embed the JAAS configuration itself in the configuration property ``sasl.jaas.config``, or whatever is the client's prefixed configuration property for ``sasl.jaas.config``. For example: 

.. sourcecode:: bash

   sasl.jaas.config=org.apache.kafka.common.security.plain.PlainLoginModule required \
      username="confluent" \
      password="confluent-secret";

If a client specifies both the client property ``sasl.jaas.config`` and the static JAAS configuration system property ``java.security.auth.login.config``, the client property ``sasl.jaas.config`` will be used.


.. _kafka_sasl_jaas_c3:

JAAS and Confluent Control Center
'''''''''''''''''''''''''''''''''''''''''''

There is one scenario when you should explicitly use the client property ``sasl.jaas.config`` instead of passing in the JVM argument ``-Djava.security.auth.login.config=/path/to/jaas.config``, and that is when you are using Confluent Control Center that has its own Kafka cluster separate from the production cluster being monitored, and the security profile differs between the two clusters.

If you were to use ``java.security.auth.login.config``, it would set a single configuration for the whole JVM for communicating to the production cluster being monitored as well as the cluster backing Control Center. This may be undesirable because this wouldn't distinguish security profiles to each cluster.

Instead, use the client property to differentiate the security profiles, i.e., different JAAS configurations, depending on the target cluster:

* production cluster: e.g., ``sasl.jaas.config``
* monitoring cluster: for Confluent Metrics Reporter use ``confluent.metrics.reporter.sasl.jaas.config``, and for Confluent Monitoring Interceptors use ``confluent.monitoring.interceptor.sasl.jaas.config``.


.. _kafka_sasl_multi_mechanisms:

Enabling multiple SASL mechanisms
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Multiple SASL mechanisms can be enabled on the broker simultaneously while each client has to choose one mechanism. 

Specify the configuration for the login modules of all enabled mechanisms in the ``KafkaServer`` section of the broker JAAS config file. For example:

.. sourcecode:: bash

   KafkaServer {
     com.sun.security.auth.module.Krb5LoginModule required
     useKeyTab=true
     storeKey=true
     keyTab="/etc/security/keytabs/kafka_server.keytab"
     principal="kafka/kafka1.hostname.com@EXAMPLE.COM";

     org.apache.kafka.common.security.plain.PlainLoginModule required
     username="admin"
     password="admin-secret"
     user_admin="admin-secret"
     user_alice="alice-secret";
  };

Enable the SASL mechanisms in ``server.properties``:

.. sourcecode:: bash

   # List of enabled mechanisms, can be more than one
   sasl.enabled.mechanisms=GSSAPI,PLAIN

Specify the SASL security protocol and mechanism for inter-broker communication in ``server.properties`` if required:

.. sourcecode:: bash

   # Configure SASL_SSL if SSL encryption is enabled, otherwise configure SASL_PLAINTEXT
   security.inter.broker.protocol=SASL_SSL

   # Configure the appropriate inter-broker protocol
   sasl.mechanism.inter.broker.protocol=GSSAPI


Then follow the mechanism-specific steps in :ref:`GSSAPI <sasl_gssapi_broker>`, :ref:`SCRAM <sasl_scram_broker>`, and :ref:`PLAIN <sasl_plain_broker>` to configure SASL for the enabled mechanisms.


Modifying SASL mechanisms in a Running Cluster
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The SASL mechanisms can be modified in a running cluster using the following sequence:

1. Enable new SASL mechanism by adding the mechanism to ``sasl.enabled.mechanisms`` in ``server.properties`` for each broker. Update JAAS config file to
   include both mechanisms as described :ref:`here <kafka_sasl_multi_mechanisms>`. Incrementally restart the cluster nodes, taking into consideration the recommendations for doing :ref:`rolling restarts <rolling_restart>` to avoid downtime for end users..
2. Restart clients using the new mechanism (if required).
3. To change the inter-broker communication mechanism (if required), set ``sasl.mechanism.inter.broker.protocol`` in ``server.properties`` to the new mechanism and
   incrementally restart the cluster again.
4. To remove the old mechanism (if required), remove the old mechanism from ``sasl.enabled.mechanisms`` in ``server.properties`` and remove the entries for the
   old mechanism from JAAS config file. Incrementally restart the cluster again.

Note that the sequence above is somewhat complex to cater for all possible mechanism changes. For example, to add a new mechanism in the brokers and swap the clients to use it, you would simply have to do steps 1 and 2.