Using Client Authentication with Kafka

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Using Client Authentication with Kafka

If you want to expose your Kafka brokers so that external clients can communicate with them, it is important to make sure that your implementation is secure. In some situations, this means implementing client authentication. In this lab, you will have the opportunity to work hands-on with one of the client authentication methods available in Kafka: client certificates. You will implement authentication with client certificates in an existing cluster, and then authenticate as a client to verify that your implementation works. This will give you hands-on experience with the process of securing a Kafka cluster.

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Lab Info

Level

Intermediate

Last updated

Sep 17, 2025

Duration

30m

Challenge

Generate Your Client Certificate Files

Generate a client certificate. Choose a password for the client keystore when prompted:

cd ~/certs/

keytool -keystore client.keystore.jks -alias kafkauser -validity 365 -genkey -keyalg RSA -dname "CN=kafkauser, OU=Unknown, O=Unknown, L=Unknown, ST=Unknown, C=Unknown"

Sign the key, then import the certificate authority and signed key into the keystore. When asked for the password to the ca-key, enter the password AllTheKeys:

keytool -keystore client.keystore.jks -alias kafkauser -certreq -file client-cert-file

openssl x509 -req -CA ca-cert -CAkey ca-key -in client-cert-file -out client-cert-signed -days 365 -CAcreateserial

keytool -keystore client.keystore.jks -alias CARoot -import -file ca-cert

keytool -keystore client.keystore.jks -alias kafkauser -import -file client-cert-signed

Move the client keystore into an appropriate location:

sudo cp client.keystore.jks /var/private/ssl/

sudo chown root:root /var/private/ssl/client.keystore.jks

Challenge

Enable Client Authentication for the Broker
1. Set client authentication to required in server.properties:
```
sudo vi /etc/kafka/server.properties
```
1. Locate the line that begins with ssl.client.auth and change it:
```
ssl.client.auth=required
```
1. Restart Kafka and then verify that everything is working:
```
sudo systemctl restart confluent-kafka

sudo systemctl status confluent-kafka
```

Challenge

Add Client Authentication Settings to Your Client Config File

Edit client-ssl.properties:

cd ~/

vi client-ssl.properties

Add the following lines:

ssl.keystore.location=/var/private/ssl/client.keystore.jks
ssl.keystore.password=<your client keystore password>
ssl.key.password=<your client key password>

Create a console consumer using client authentication to make verify that everything is working:

kafka-console-consumer --bootstrap-server zoo1:9093 --topic inventory_purchases --from-beginning --consumer.config client-ssl.properties

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