emqx4.3/apps/emqx/rebar.config.script

IsCentos6 = fun() ->
                case file:read_file("/etc/centos-release") of
                    {ok, <<"CentOS release 6", _/binary >>} ->
                        true;
                    _ ->
                        false
                end
            end,

IsWin32 = fun() ->
                win32 =:= element(1, os:type())
          end,

IsQuicSupp = fun() ->
                not (IsCentos6() orelse IsWin32() orelse
                     false =/= os:getenv("BUILD_WITHOUT_QUIC")
                    )
             end,

Bcrypt = {bcrypt, {git, "https://github.com/emqx/erlang-bcrypt.git", {branch, "0.6.0"}}},
Quicer = {quicer, {git, "https://github.com/emqx/quic.git", {branch, "0.0.9"}}},

ExtraDeps = fun(C) ->
                {deps, Deps0} = lists:keyfind(deps, 1, C),
                Deps = Deps0 ++ [Bcrypt || not IsWin32()] ++
                [ Quicer || IsQuicSupp()],
                lists:keystore(deps, 1, C, {deps, Deps})
            end,

ExtraDeps(CONFIG).