I am using the JavaScript SDK to authenticate Stack Exchange users in our application. But the dialog stays in "Authorizing Application" page, as I found there is a error thrown in this page:

Uncaught TypeError: Cannot read property 'postMessage' of null
    at HTMLDocument.<anonymous> (login_success?assisted=16699&protocol=http&proxy=http%3a%2f%2flocalhost%3a8080%2fblank.html:217)

As the login demo works fine on my side, but the issue consists throwing this issue.

Thanks in advance for any help.