Ok, I use plain Text auth for success test. I copied the output of this command to the client.properties:

kubectl get secret kafka-user-passwords --namespace kafka -o jsonpath='{.data.client-passwords}' | base64 -d | cut -d , -f 1

And the client.properties file looks like this:

security.protocol=SASL_PLAINTEXT
#sasl.mechanism=SCRAM-SHA-256
sasl.mechanism=PLAIN
sasl.jaas.config=org.apache.kafka.common.security.plain.PlainLoginModule required username="user1" password="OUTPUT_OF_GET_SECRET";