I bought this cabinet door lock
from Ace hardware and made it work on my slider canopy. I drilled
a hole through the side skirt that was aligned with a hole in the
aluminum skirt prace.
Here you can see the lock from the inside.
I then cut a notch in the canopy rail for
the arm on the lock to rotate into when locked.
Here is the lock from the outside.
This turned out to be a pretty simple job.