Bathroom Cabinet Wiring - Electrician Question

[Pickled Piper]

I am hoping any Electricians on line can help. My Sparky kindly left me the necessary mains wiring protruding though a stud wall ready for a cabinet to be fitted. I now have the cabinet in place and this has a flex coming out from it. How do I join the flex and mains wiring? Is there a specific type of connectorl I need given that it's in a bathroom? or can I use a strip connector and push the joint back into the stud wall?

Many thanks in advance.

[Pickled Piper]

Cheers, I got a chocbox thing. Actually debox from screwfix.

Wiring provided by the Sparky is all good. It's in the lighting circuit and rcd protected.