With the Leica rangefinder it is all manual focus, in fact I use manual for all my settings on the Leica. This is part of the fun and challenge with shooting essentially 1950's technology. But this can be frustrating with street shots as the action is quick. I have found that zone focusing works well, although best in bright light to keep at f8 or f16. I also use ISO of 3200, delighted with a little grain.
Pro tip: This shot happened in a split second, I need to be dialed in on the camera to anticipate these moments. As I move, so does the light, thus new settings.