Connect to two database one wordpress and other xenforo

Connect to two database one wordpress and other xenforo I want my visitors to register new accounts using xenforo registration and can use that login info to log in wordpress i need when that user register using xenforo registration to add same info to wordpress database so he can login with same username and password in two website (wordpress & xenforo) and this is an example [login to view URL] <--wordpress [login to view URL] <--xenforo