In order to connect your When I Work account in Grow, you will need your username, password, and a private developer key in order to access their API.
If you haven't already, you will need to request a dev key. This can be done by going to http://dev.wheniwork.com/.
If you scroll down to the bottom of the pane on the left-hand side, you will see a link at the very bottom labeled "Sign up for a Developer Key." Clicking on this link will open up an email that you will need to fill out to request a key.
Here is a gif that shows you the process:
After you have your developer key, go ahead and copy it into Grow and press submit. Your When I Work account is now connected.
Questions? Let us know at email@example.com or chat in on the site.