Buying online - request for DoB

I was just going to buy online from a UK site I hadn't used before and when it came to checkout they requested my date of birth - stated on the form to be for credit card authorisation (it's not a banned or dodgy product!!). I've never had to give this level of detail before - think it sounds fishy?

I've just bought a gift using visa debit, this asks your date of birth when it authenticates the card

You should not have to provide such data.

That is normal where it will ask for selected characters from your password.

The site you are buying from should not be seeing this information.