Cat flap in greenhouse door?

Has anyone managed to put a cat flap in their greenhouse door? Long story short, neighbour's cat has taken to living in our greenhouse, mainly because he doesn't like their 10 (!) other cats and various dogs ..... We are happy for him to come and go as he pleases and he has a warm box in there to sleep in if need be (the neighbour knows he is here), but obviously with winter about to set in properly it's too cold to leave the door ajar, both for the cat and for the plants that are in there. Has anyone put a cat flap in a greenhouse door? I've googled it but it doesn't come up with much, other than some guy who put a homemade "out" only cat flap in so cats didn't get trapped inside his. Thanks in advance.
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https://www.petplanet.co.uk/p20926/pet_tek_glass_fitting_dual_glaze_clear.aspx?ptm_source=google&ptm_medium=shopping&ptm_campaign=under10_65736&campaign=18028239734&adgroup=&keyword=&gclid=EAIaIQobChMIoMSRiNbQ-wIVBpftCh3i0gCCEAYYAyABEgIUyPD_BwE
The main problem will be cutting a hole in the door. Unless the “glass” is plastic you will probably come up against safety glass, which shatters rather than cuts into pieces. You may have to order a sheet of plastic for the door too. I don’t recommend horticultural glass. Deadly stuff.
My answer is send it home.
'The power of accurate observation .... is commonly called cynicism by those that have not got it.
George Bernard Shaw'
Does your cat have an absolute favourite food? Our new cat would sell her soul for a thin shaving of gjetöst cheese.
We stuck tiny bits of it round the flap so that she became accustomed to the noise when her head got close to the flap.
After a few days (and quite a bit of cheese) she finally managed to go through it. 😊