Config dump on error leaks credentials

[chrooti]

When the config is dumped, which happens when e.g. Kaffe can't connect to the Kafka cluster, the whole producer/consumer keyword list is written to stdout, credentials included.

It's not really a library issue per se, but I thought I'd raise it just in case (maybe a warning in the README is enough).

[foo-1a]

would like to chip in with further detail here - what we're observing is that when part of configuration is not provided to producer, this leads to a Elixir.KeyError being returned from Kaffe:start/1, making it non-conformant to the expected error return value as per behaviour doc of {error, term()}.
This causes the full term being logged as a result of a supervisor start failure, and in particular the partial consumer config containing credentials.

In our case this is being triggered by virtue of having a phoenix config/runtime.exs configuration always configuring kaffe's producer credentials (thus creating config :kaffe {producer: [sasl: #{..creds..}]}, but then not adding the configuration for endpoints in one specific deployment environment where we were not intending to connect to kafka.
This leads kaffe to attempt configuration of a producer, but failure to find the endpoints key from producer: [...] before setting up its own supervisor.

If you think that the case is weird b/c of the way we're configuring the lib that's legit - but I'd still suggest that adapting the error so that Kaffe:start/1 returns {error, term()} and/or redacting the sasl: #{...} term when present, as it is known to contain credentials, could be beneficial.

Observed stacktrace, with some formatting:

Kernel pid terminated (application_controller) (
  {application_start_failure,kaffe,
    {bad_return,
      {
        {'Elixir.Kaffe',start,[normal,[]]},
        {'EXIT',
          {
            #{'__exception__' => true,
              '__struct__' => 'Elixir.KeyError',
              key => endpoints,
              message => nil,
              term => [
                {sasl,
                  #{login => <<"REDACTED">>,mechanism => plain,password => <<"REDACTED">>}
                }
              ]
          },[
            {'Elixir.Keyword','fetch!',2,[{file,"lib/keyword.ex"},{line,595}]},
            {'Elixir.Kaffe.Config.Producer',endpoints,0,[{file,"lib/kaffe/config/producer.ex"},{line,20}]},
            {'Elixir.Kaffe.Config.Producer',configuration,0,[{file,"lib/kaffe/config/producer.ex"},{line,6}]},
            {'Elixir.Kaffe.Producer',start_producer_client,0,[{file,"lib/kaffe/producer.ex"},{line,50}]},
            {'Elixir.Kaffe',start,2,[{file,"lib/kaffe.ex"},{line,19}]},
            {application_master,start_it_old,4,[{file,"application_master.erl"},{line,293}]}]}}}}})