Private bitbucket repository as npm dependency In a way that it still works in your choice of Continuous Integration tools.
The Hard Way By using BitBucket’s SSH deployment keys.
Tom Spencer has written a great post about this and I’ve used his method succesfully.
There’s nothing wrong his this approach, I just found it very complicated (for my specific use case) because it requires generating SSH keys, setting them up in BitBucket, and adding extra scripts in your dependant project that set up the SSH keys in the build environment before it can execute npm install.