Demonstration of a bug in Faraday. The adapters all treat a header with multiple values differently.

client.rb

require 'net/http'

response = Net::HTTP.new('localhost', 4567).send_request('GET', '/')
puts response.get_fields('Set-Cookie').inspect

result

$ ruby client.rb   
["foo", "bar"]

server.rb

require 'sinatra'

get '/' do
  [200, { 'Set-Cookie' => %w[ foo bar ] }, '']
end