Oauth2 get_token test with rspec

I am creating a controller spec for the get_token part of oauth2 authentication. At this point the user has authorized my application and I need to generate and save a token and other information. Rspec is failing with some cryptic error.

Failure/Error: get :auth, { code: "auth_code", scope: "read_write" }
     OAuth2::Error:
       {:token_type=>"bearer", 
        :stripe_publishable_key=>"PUBLISHABLE_KEY", 
        :scope=>"read_write", 
        :livemode=>"false", 
        :stripe_user_id=>"USER_ID",  
        :refresh_token=>"REFRESH_TOKEN", 
        :access_token=>"ACCESS_TOKEN"}

      

        
        
        
      

    

Here is the controller code. Rspec says it doesn't work for get_token.

require 'oauth2'

def auth
  code = params[:code]
  client = oauth_client
  token_response = client.auth_code.get_token(code, params: { scope: 'read_write' })
  token = token_response.token

      

        
        
        
      

    

And here's the test. The webmock must intercept get_token. This is an autogenerated webmock suggested by rspec that I have filled in the body with the appropriate request and response body.

before do
  stub_request(:post, "https://connect.stripe.com/oauth/token").
    with(:body => {"client_id"=>"CLIENT_ID",
                   "client_secret"=>"SOME_SECRET",
                   "code"=>"auth_code",
                   "grant_type"=>"authorization_code",
                   "params"=>{"scope"=>"read_write"}},
         :headers => {'Accept'=>'*/*',
                      'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
                      'Content-Type'=>'application/x-www-form-urlencoded',
                      'User-Agent'=>'Faraday v0.9.0'}).
    to_return(:status => 200,
              :body => {token_type: "bearer",
                        stripe_publishable_key: "PUBLISHABLE_KEY",
                        scope: "read_write",
                        livemode: "false",
                        stripe_user_id: "USER_ID",
                        refresh_token: "REFRESH_TOKEN",
                        access_token: "ACCESS_TOKEN"},
              :headers => {})
end

describe "#auth" do
  it "creates a payment gateway" do
    get :auth, { code: "auth_code", scope: "read_write" 
  end
end

      

        
        
        
      

    

This process already works in practice, so at least the controller code is not at fault. What am I doing wrong?