Add a new configuration to specify the path to the kerberos ticket cache

[makotonakai]

I'm trying to establish multiple kerberos authentication for different principals in the same fluentbit.

[OUTPUT]
  Name Kafka
  Match app
  Brokers broker-1:9092, broker-2:9092
  Topics topic-1
  rdkafka.security.protocol sasl_ssl
  rdkafka.ssl.ca.locaiton /to/path/to/ca_file
  rdkafka.kerberos.service name service-name-1
  rdkafka.sasl.mechanism GSSAPI
  rdkafka.sasl.kerberos.keytab /to/path/to/keytab-1
  rdkafka.sasl.kerberos.principal principal-1
  rdkafka.sasl.kerberos.kinit.cmd kinit -V -R -t "/to/path/to/keytab-1" -k principal-1 -c "/to/path/to/cache-1"

[OUTPUT]
  Name Kafka
  Match app
  Brokers broker-1:9092, broker-2:9092
  Topics topic-2
  rdkafka.security.protocol sasl_ssl
  rdkafka.ssl.ca.locaiton /to/path/to/ca_file
  rdkafka.kerberos.service name service-name-2
  rdkafka.sasl.mechanism GSSAPI
  rdkafka.sasl.kerberos.keytab /to/path/to/keytab-2
  rdkafka.sasl.kerberos.principal principal-2
  rdkafka.sasl.kerberos.kinit.cmd kinit -V -R -t "/to/path/to/keytab-2" -k principal-2 -c "/to/path/to/cache-2"

However, I got the following logs.

Using specified cache: /to/path/to/cache-1
Using principal: principal-1
Using keytab: /to/path/to/keytab
Authenticated to Kerberos v5

Using specified cache: /to/path/to/cache-2
Using principal: principal-2
Using keytab: /to/path/to/keytab
Authenticated to Kerberos v5
...

No credentials were supplied, or the credentials were unavailable or inaccessible (No Kerberos credentials available (default cache: FILE:/tmp/krbcc_0)

This happens because the default location is referred, even though the ticket caches are created in different locations.

It would be nice if there is an option to specify the location of the ticket cache (e.g. rdkafka.sasl.kerberos.cache.location) for each authentication.