@David Hamilton Here's an example of how to combine list of filters in a functional fashion:

val defaultStack = Filter.NoOp.then(ClientFilters.GZip())

    val additionalFilters: List<Filter> = listOf(
        DebuggingFilters.PrintRequestAndResponse(),
        ClientFilters.BasicAuth("user", "pass"))

    // additional after default
    val combinedFilter1: Filter = additionalFilters.fold(defaultStack) { acc, next -> acc.then(next) }
    
    // additional before default
    val combinedFilter2: Filter = additionalFilters.fold(Filter.NoOp) { acc, next -> acc.then(next) }.then(defaultStack)

You even answered the unspoken question of whether the filters should be added before or after the existing stack

They can be added in either order. It depends on how your default stack is supposed to be used by each service really

Slight mod here: reduce() would be a slightly more appropriate function to use (over fold()), as the input and output types of the accumulator function are identical (both Filter). Doesn’t really matter which you use, but is slightly more FP-tastic 🙃