getting a cookie to work

[lsiden <lsiden@gmail.com>]

My Sinatra app sets a cookie whose value is 'myapp.heroku.com', then
redirects:

     CALC_URL = 'http://localhost:4020/alc'

      domain = ENV['URL'] || 'localhost'
      logger.info "cookie domain=#{domain}"
      response.set_cookie 'session_id', {
        :value => session_id,
        :domain => domain,
        :path => '/',
      }

      redirect CALC_URL

Here is the log message:

  INFO -- : cookie domain=myapp.heroku.com

But when I examine the cookie with Firebug, it's domain is
'.myapp.heroku.com', not 'myapp.heroku.com'.  In other words,
something has added a dot in front of the domain.  And when the app
makes an AJAX call to myapp.heroku.com, the cookie is not included,
and therefor it fails.

Can anyone tell me where the dot is coming from and what I need to do
so that the browser will send the cookie when it makes requests to
myapp.heroku.com?