Without being able to see the code behind that window I couldn't say for sure what method is being used. However; it does not look like it is using oAuth 2. I am just guessing, but it is probably using a URL to request the Access Token. If you can look at the code you will probably see the information being sent.
I would suggest setting up your application to take advantage of oAuth 2 and you can find that documentation located here. http://developer.constantcontact.com/docs/authentication/authentication.html
If you just need to get an Access Token you can also retrieve that data using our I/O Docs located here. https://constantcontact.mashery.com/io-docs
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