Is it thread safe to set Active Resource HTTP authentication on a per-user basis?

Active Resource can make use of HTTP authentication set at the class level. For instance:

class Resource < ActiveResource::Base
end

Resource.user = 'user'
Resource.password = 'password'

or

Resource.site = "http://user:password@site.com/"

But what if I use different HTTP authentication based on which user is logged in? If I change Resource.user and Resource.password, is that going to cause a race condition where requests from one thread suddenly start using the authentication of a user whose requests are running simultaneously in a different thread? Or is this a non-issue (as long as I reset the authentication between requests) because rails servers are not multithreaded?

Even if there's no thread safety problem, it still seems risky that if I fail to reset them, the previous user's credentials will be used automatically by future requests.

Update: After being frustrated with ActiveResource, I wrote my own REST library: https://github.com/DeepWebTechnologies/well_rested

Monkey patch the host, user and password methods of ActiveResource::Base class:

class ActiveResource::Base
  # store the attribute value in a thread local variable
  class << self
    %w(host user password).each do |attr|               

      define_method(attr) do
        Thread.current["active_resource.#{attr}"]
      end

      define_method("#{attr}=") do |val|
        Thread.current["active_resource.#{attr}"] = val
      end
    end
  end
end

Now set the credentials in every request

class ApplicationController < ActionController::Base

  around_filter :set_api_credentials

private 

  # set the credentials in every request
  def set_api_credentials
    ActiveResource::Base.host, 
      ActiveResource::Base.user, 
        ActiveResource::Base.password = current_user_credentials
    yield
  ensure
    ActiveResource::Base.host = 
      ActiveResource::Base.user = 
        ActiveResource::Base.password = nil
  end

  DEFAULT_HOST, DEFAULT_USER, DEFAULT_PASSWORD= [
    "http://www.foo.com", "user1", "user78102" ]

  def current_user_credentials
    current_user.present? ? 
      [ current_user.host, current_user.login, current_user.password] : 
      [ DEFAULT_HOST, DEFAULT_USER, DEFAULT_PASSWORD]
  end

end