The door's joints are loose as a goose. Take the door off the hinges
and pull the door completely apart. It will no doubt come apart
easily, more easily than you think.
There is likely 2 dowels holding each of the joints together. Remove
those dowels, clean them and reuse them, unless they are rotten,
broken or something else wrong with them. Replace any dowels with new
ones and/or larger dowels, if need be. For larger dowels, drill their
mating holes larger.
Clean up all the mating glue edges and reglue the door together using
a water proof glue (Titebond III water proof glue). Don't apply glue
to the panels... allow them to float freely in the framing.
To completely disassemble, clean up the edges and reglue the door will
be a lot easier than you think.... and prevent later headaches with
Those glass panes should be easy to remove, also. If they have putty
on both sides, you might want to replace the putty with wood molding
with clear silicone caulking to seat the panes. If you replace the
putty, seal the inner raw edges of the framing, either with primer/
paint/clearcoat, before reinstalling the panes.