title: spring-kafka application.properties configuration for JAAS/SASL not working
body: <p><b>Use Case:</b><br>
  I am using Spring Boot <code>2.2.5.RELEASE</code> and <code>Kafka 2.4.1</code><br>
  JAAS/SASL configurations are done properly on Kafka/ZooKeeper as topics are created without issue with <code>kafka-topics.bat</code><br></p>
  
  <p><b>Issue:</b><br>
  When i start Spring Boot application, i immediately get the following errors:<br></p>
  
  <p>kafka-server-start.bat console:<br>
  <code>INFO [SocketServer brokerId=1] Failed authentication with /127.0.0.1 (Unexpected Kafka request of type METADATA during SASL handshake.) (org.apache.kafka.common.network.Selector)</code></p>
  
  <p>IDE console:<br>
  <code>WARN  org.apache.kafka.clients.NetworkClient - [Consumer clientId=xxx, groupId=yyy] Bootstrap broker localhost:9093 (id: -3 rack: null) disconnected</code></p>
  
  <p>My <code>application.properties</code> configuration:</p>
  
  <pre><code>spring.kafka.jaas.enabled=true
  spring.kafka.properties.security.protocol=SASL_PLAINTEXT
  spring.kafka.properties.sasl.mechanism=PLAIN
  spring.kafka.properties.sasl.jaas.config=org.apache.kafka.common.security.plain.PlainLoginModule required username="spring_bO0t" password="i_am_a_spring_bO0t_user";
  </code></pre>
  
  <p><code>kafka_server_jaas.conf</code>:</p>
  
  <pre><code>KafkaServer {
      org.apache.kafka.common.security.plain.PlainLoginModule required
      username="admin"
      password="12345"
      user_admin="12345"
      user_spring_bO0t="i_am_a_spring_bO0t_user";
  };
  </code></pre>
  
  <p>Am i missing something?</p>
  
  <p>Thanks in advance.</p>