I've seen a few other SO questions that are related to this; but I've been through all of the fixes with no joy.
My company had one Mac for use for the team. This worked absolutely fine. We really needed another so we have another. I exported the developer profile from the first Mac on to the second Mac. This seemed to work fine, we can test on local devices, etc. However, now we cannot upload on to the App Store from either Mac- they just get stuck on authentication with no error.
Things I've done:
- Tried a different connection
- Set the HTTPS proxy port to 80
- Run the application loader and XCode at the same time
- Regenerate our certificates and provisioning profiles
- Set the build settings to various combinations of certificates and profiles
- Turn it off and on again (more than once)
- Update Java
- Bump version and build numbers
- Checked the licence agreement (no updates)
- Deleted the XCode DerivedData caches
I can access the Apple developer sites just fine- developer.apple.com, the iTunes Connect stuff, all of that without trouble.