Stuck on "Authenticating with iTunes Store"

https://forums.developer.apple.com/thread/76803

Try this, it fixed it for me. Open Terminal and run:

1. cd ~
2. mv .itmstransporter/ .old_itmstransporter/
3. "/Applications/Xcode.app/Contents/Applications/Application Loader.app/Contents/itms/bin/iTMSTransporter"

iTMSTransporter will then update itself, then you can try uploading in XCode again.