Handling Multiple User Authentication With ActiveResource Clients

I'm in the process of building a REST service using rails and ActiveResource. On the server side everything was fairly straightforward, but I hit a snag when I moved to the web tier. For various reasons I wanted to have two separate servers, one providing the REST service and the other serving HTML content. The rub is that ActiveResource assumes that credentials are a class level attribute. I'd like the calls to the ActiveResource client to use the credentials of the currently logged on user, but there doesn't appear to be a straightforward way to do this out of the box. Metaprogramming to the rescue!

Using the REST example from my last post, I extended the client in the following way.

require 'activeresource'

module Sample
  module Client
    class API
      #
      # Creates a module that serves as an ActiveResource
      # client for the specified user
      #
      def self.create_api(login = nil, password = nil)
        # specify the site.  Default to no credentials
        @url_base = "http://localhost:3000"
        @url_base = "http://#{login}:#{password}@localhost:3000" if login
        # build a module name.  This assumes that logins are unique.
        # it also assumes they're valid ruby module names when capitalized
        @module = login ? login.capitalize : "Default"
        class_eval <<-"end_eval",__FILE__, __LINE__
        module #{@module}
          class Post < ActiveResource::Base
            self.site = "#{@url_base}"
          end
          class Comment < ActiveResource::Base
            self.site = "#{@url_base}/posts/:post_id"
          end
          # return the module, not the last site String
          self
        end
        end_eval
      end
    end
  end
end

This new version allows you to create an api for a specific user. You can squirrel this away and use it for specific users, allowing you to use multiple connections to your rest service. A quick irb session follows

>> require 'ares_sample_client'
=> ["Sample"]
>> api = Sample::Client::API.create_api
=> Sample::Client::API::Default
>> p = api::Post.find(1)
=> #<Sample::Client::API::Default::Post:0xb715af74 @attributes={"updated_at"=>Wed Jan 09 02:36:34 UTC 2008, "id"=>1, "content"=>"The first post", "user_id"=>1, "created_at"=>Wed Jan 09 02:36:34 UTC 2008}, @prefix_options={}>
>> p = api::Post.create(:content => "should fail")
ActiveResource::UnauthorizedAccess: Failed with 401 Unauthorized
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/connection.rb:125:in `handle_response'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/connection.rb:112:in `request'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/connection.rb:101:in `post'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/base.rb:803:in `create'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/base.rb:636:in `save_without_validation'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/validations.rb:262:in `save'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/base.rb:339:in `create'
        from /usr/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/core_ext/object/misc.rb:28:in `returning'
        from /usr/lib/ruby/gems/1.8/gems/activeresource-2.0.2/lib/active_resource/base.rb:339:in `create'
        from (irb):4
>> auth_api = Sample::Client::API.create_api('test1','test1')
=> Sample::Client::API::Test1
>> p = auth_api::Post.find(1)
=> #<Sample::Client::API::Default::Post:0xb713dde8 @attributes={"updated_at"=>Wed Jan 09 02:36:34 UTC 2008, "id"=>1, "content"=>"The first post", "user_id"=>1, "created_at"=>Wed Jan 09 02:36:34 UTC 2008}, @prefix_options={}>
>> p = auth_api::Post.create(:content => "should succeed!")
=> #<Sample::Client::API::Test1::Post:0xb713312c @attributes={"updated_at"=>Thu Jan 10 04:01:53 UTC 2008, "id"=>7, "content"=>"should succeed!", "user_id"=>nil, "created_at"=>Thu Jan 10 04:01:53 UTC 2008}, @prefix_options={}>
>>