I put my Macbook Pro in for a screen repair today at the Genius bar and I had to give them my login password. Is this normal?

How else would the be able to log in? Yes it is normal but the better way would have been to either create another user on the computer and give them that password or you could have removed all your data then give them the computer and password. In any case, I hope you made a backup of your hard drive in case they have to reformat it or otherwise destroy your data.

Keeping your confidential data secure during hardware repair