Happy to hear this! 
A few notes for completeness: 
First is it “myapp://callback” or “myapp”?
myapp is the scheme; myapp://callback is the URI.
You register the scheme in your manifest file in order to make the operating system call your app when an URL with this scheme is called. Your manifest file is correct.
how can I close the browser after the user logs in for example the desktop app on Windows?
You can’t at the moment. Unfortunately, this depends on the WebAuthenticator running on Windows.
it should be “myapp://callback/ ” not something like “myapp://callback ”
Yes. The trailing slash is required. BTW, this is required only on Windows, but if you are building a cross-platform app, you need to stick with it.