Cannot modify `request.params` in before(:all) block.

test.rb

# Given this auth helper in spec/support/ directory...
module AuthHelpers
  def add_token_to_params(token)
    request.params.merge!({sessionToken: token}) # also tried 'request.params[:sessionToken] = token'
  end
end

# Given this test...
class ThingController
  describe Thing do
    before(:all) do
      @user = User.authenticate(Settings.tests.user, Settings.tests.password)
      @token = @user.attributes["sessionToken"]
    end
    
    describe "attempt to create Thing without session token" do
      before(:each) { add_token_to_params(@token) } # Yes, I did inspect it here, the @token has a valid value. ;)

      it "should fail" do
        puts request.params # Shows {"sessionToken"=>"abc"}
        post :create, attr1: 1, attr2: 'abc'  # etc.
        puts request.params # Shows {"attr1"=>1, "attr2"=>"abc"}
        # failure here; my application_controller before_filter that enforces the presence of
        # the 'sessionToken' parameter kicks in and returns '401 Unauthorized'.
        response.should be_success
      end
    end
  end
end

# ...I want to freely modify request parameters before invoking controller actions.
# (I know I can modify the headers, btw; tried it and it works.)
# I am 99% certain I am doing it the wrong way, but couldn't find anything in Google
# that actually covers my requirements.

# The problem is not just to make this work in one "it" block; I have dozens of mini tests.
# I know I can make this work using simpler methods for just one "it" block, but that's not my scenario.

That did it. I am just not that well familiarized with the RSpec lingo yet. Thanks a lot for your support, it's highly appreciated. =)