Pulsar: Please check your java.security.login.auth.config (=null) for section header: PulsarBroker

1. pulsar集群版本为2.7.0
2. pulsar配置了基于kerberos的安全认证
3. 在conf/broker.conf文件里配置了saslJaasBrokerSectionName=MQBroker
4. 在jaas文件中部分配置如下：

MQBroker {
   com.sun.security.auth.module.Krb5LoginModule required
   useKeyTab=true
   storeKey=true
   useTicketCache=false
   keyTab="${pulsar_keytab_path}/${broker_server_keytab_name}"
   principal="broker/REPLACE_HN@${krb5_realm}";
};
.........

broker启动后，报错如下：

20:52:23.227 [main] ERROR org.apache.pulsar.common.sasl.JAASCredentialsContainer - No JAAS Configuration section header found for Client: loginContext name (JAAS file section header) was null. Please check your java.security.login.auth.config (=null) for section header: PulsarBroker
20:52:23.227 [main] ERROR org.apache.pulsar.broker.authentication.AuthenticationProviderSasl - JAAS login in broker failed
javax.security.auth.login.LoginException: loginContext name (JAAS file section header) was null. Please check your java.security.login.auth.config (=null) for section header: PulsarBroker
        at org.apache.pulsar.common.sasl.JAASCredentialsContainer.(JAASCredentialsContainer.java:69) ~[org.apache.pulsar-pulsar-common-2.7.0.jar:2.7.0]
        at org.apache.pulsar.broker.authentication.AuthenticationProviderSasl.initialize(AuthenticationProviderSasl.java:88) [org.apache.pulsar-pulsar-broker-auth-sasl-2.7.0.jar:2.7.0]
        at org.apache.pulsar.broker.authentication.AuthenticationService.(AuthenticationService.java:57) [org.apache.pulsar-pulsar-broker-common-2.7.0.jar:2.7.0]
        at org.apache.pulsar.broker.service.BrokerService.(BrokerService.java:305) [org.apache.pulsar-pulsar-broker-2.7.0.jar:2.7.0]
        at org.apache.pulsar.broker.PulsarService.start(PulsarService.java:463) [org.apache.pulsar-pulsar-broker-2.7.0.jar:2.7.0]
        at org.apache.pulsar.PulsarBrokerStarter$BrokerStarter.start(PulsarBrokerStarter.java:277) [org.apache.pulsar-pulsar-broker-2.7.0.jar:2.7.0]
        at org.apache.pulsar.PulsarBrokerStarter.main(PulsarBrokerStarter.java:346) [org.apache.pulsar-pulsar-broker-2.7.0.jar:2.7.0]

1. 虽然配置sectionName为MQBroker，但是貌似配置没生效，还是用的默认SectionNamePulsarBroker
2. 查看源码文件pulsar-broker-commonsrcmainjavaorgapachepulsarbrokerServiceConfiguration.java，注：版本为2.7.0，发现如下源码

@FieldContext(
        category = CATEGORY_SASL_AUTH,
        doc = "Service Principal, for login context name. Default value is "PulsarBroker"."
    )
    private String saslJaasServerSectionName = SaslConstants.JAAS_DEFAULT_BROKER_SECTION_NAME;

3. 查看源码可发现，Broker加载配置时，加载的是配置项是saslJaasServerSectionName，而不是saslJaasBrokerSectionName，估计是一个小bug。

方案一：
将broker.conf文件中的配置项改为由saslJaasBrokerSectionName改为saslJaasServerSectionName

方案二
将源码pulsar-broker-commonsrcmainjavaorgapachepulsarbrokerServiceConfiguration.java中相关的配置项由saslJaasServerSectionName改为saslJaasBrokerSectionName，重新编译源码后将相关jar包替代集群中对应的lib包。

方案一较简单，亲测可行；
方案二较麻烦，没有亲自测试，但是理论上应该是可以的。