How can I connect Aweber to my Rails app using OAuth?

I'm trying to integrate my Rails app with Aweber via OAuth, using the official aweber gem.

If I follow their flow in the Rails console, I can get an access token, no problems:

oauth = AWeber::OAuth.new(ENV["AWEBER_CONSUMER_KEY"], ENV["AWEBER_CONSUMER_SECRET"])
puts oauth.request_token.authorize_url
# => http://ift.tt/1JpWwfi

Then I visit that URL, type in my credentials, get a verification code, and go back to the rails console:

oauth.authorize_with_verifier 'xxxxxx'
# => #<OAuth::AccessToken>

Success!

The problem is, I want to do this in the real world, not just at the console, which means my Ruby code needs to be broken up into two separate actions. First, there's the controller action which redirects to Aweber's Oauth page:

def aweber
  oauth = AWeber::OAuth.new(ENV["AWEBER_CONSUMER_KEY"], ENV["AWEBER_CONSUMER_SECRET"])
  redirect_to  oauth.request_token(oauth_callback: "http://ift.tt/1H0hUKK").authorize_url
end

Then there's the action which gets the access token after the user has input their credentials and been redirected:

def aweber_callback
  oauth = AWeber::OAuth.new(ENV["AWEBER_CONSUMER_KEY"], ENV["AWEBER_CONSUMER_SECRET"])
  oauth.authorize_with_verifier(params[:oauth_verifier]) 
end

When I do it this way, the final line (authorize_with_verifier) always raises #<OAuth::Unauthorized: 401 Unauthorized>.

Seems like the problem is that I'm initializing the oauth variable twice, meaning I have two unrelated instances of AWeber::Oauth ... and only the instance of AWeber::Oauth that generated the authorize_url can get the access token. But I can't get the *same* instance in bothaweber_callbackandaweber` because I'm dealing with two completely different threads and instances of the controller.

When I inspect oauth, I can see that the internal variables oauth.request_token.params["oauth_token"] and oauth.request_token.params["oauth_token_secret"] are different in each oauth, which I'm guessing is the cause of the problem. I can get the 'correct' oauth_token from the params (params[:oauth_token]), but I can't figure out how to get the correct oauth_token_secret (not to mention that manually setting instance variables like this feels very hacky and is probably not the best approach.)

How can I generate an access token?