If you need to register for a new Intel XDK account, go here > https://software.intel.com/registration/xdk < to register and create your new account. That account can then be used to login to the Intel XDK as well as this forum and most other intel.com web sites and forums.
The incompatible certificate problem that was preventing users from logging into the Intel XDK has been resolved. Unfortunately, that certificate incompatibility is still preventing new users from registering for new Intel XDK accounts.
If you already have an Intel XDK account you can login to v3900 of the Intel XDK using your existing userid and password, the previous login workaround is no longer required!