Support for brod_gssapi and other custom brod sasl authenticators about broadway_kafka

[ramonpin]

@aravindanck our intention is to have support for the SASL_PLAINTEXT with GSSAPI at least. We probably will need to make several consecutive PRs to other erlang/kafka's ecosystem proyects used by this module.

[ramonpin]

Sorry guys some problems in other areas of the application leave me no time for this.

@aravindanck great work from your side. Where you able to make it work with brod_gssapi library?

Hoping to contribute soon.

[ramonpin]

From source code 'brod_client.ex':

  defp validate_option(:sasl, :undefined),
    do: {:ok, :undefined}

  defp validate_option(:sasl, value) do
    with {mechanism, username, password}
         when mechanism in [:plain, :scram_sha_256, :scram_sha_512] and
                is_binary(username) and
                is_binary(password) <- value do
      {:ok, value}
    else
      _value -> validation_error(:sasl, "a tuple of SASL mechanism, username and password", value)
    end
  end

I can try to make a PR adding the validation needed for the callback related tuple to that function but don't know if you expect any other problems down the stream.

[josevalim]

A PR is welcome. We can either stop validating it or validate this additional value. Both approaches are fine!

[aravindanck]

We're also looking to have this option as part of Broadway Kafka. Just curious @ramonpin - which SASL mechanism are you trying to support?

[aravindanck]

@ramonpin Is there a PR for this one already? If not, are you planning to raise one soon?

[aravindanck]

@ramonpin It should work for brod_gssapi library, as the validation check enables you to work with any SASL callback module. I tried this with a callback module built for a different SASL mechanism