Ruby's ENV::[]= only accepts strings

You cannot set the value of an environment variable to something that is not a string

# THIS DOES NOT WORK
ENV["SKIP_AUTH"] = true
=> `[]=': no implicit conversion of true into String (TypeError)

You can, however, pass an object that implements #to_str

class User < ApplicationRecord
  def to_str
    to_global_id.to_s
  end
end

ENV["user"] = User.first
ENV["user"]
=> "gid://rails-app/User/3f565b9c-0899-49f6-ab20-aa2724235ff5"

Be careful when stubbing ENV in specs:

# ENV could never return a boolean, your tests will lie to you.
RSpec.describe "ENV" do
  before do
    stub_const("ENV", {"SKIP_AUTH" => true})
  end
end