iTunes Connect is used by developers to access the application information and other content. And this is not the first time it happens, last year was more than 3 or 4 days out of service.
My recommendation is that you sign from developer.apple.com to solve some problems with iTunes Connect log in. If it worked you write a comment so that others know that it is a valid solution. Thank you.
In addition there are people who are having problems when accessing iTunes and the App Store on iOS. Although it not seems to be affecting many people compared to the panel of developers.