You can access the "Keyboard Controls" window from the top menu bar. Select Options > Configure Controls. Here's mine, with WASD movement setup in the rightmost column:
- "Move left/right" and "Sidestep" seem to do the same thing.
- "Look up/down" are bound to middle mouse scroll up/down. Toggle move mode is bound to middle mouse click.
- You can bind two keys to the same action, so I've got old arrow movement and WASD movement both in place. My WASD movement is defined in the right column in the image above.
- With WASD movement, the "Quick chat message" button becomes more useful. I believe tab is the default binding for this -- you can use it to quickly set "focus" to the chat window after you've bound letters to other actions.
- I haven't had any luck binding the "Escape" key. The Keyboard Controls dialog uses it to cancel actions, so it doesn't seem that it can be defined from here.