I assume you have shell access to your wordpress installtion here.
Go to your wordpress directory and enter: (use your own name)
htpasswd -c .htpasswd klaus
Enter your password twice and then run:
Copy the printed directory into your clipboard and replace “your directory here” from the following lines with your path.
AuthType Basic AuthName "Password Protected Area" AuthUserFile <your directory here!>/.htpasswd Require valid-user
Now open .htaccess with your preferred editor like vim and copy/paste the above lines before it says # BEGIN WordPress