Those who like sausages should not see how they are made -- Anonymous

When you are in the midst of developing a web site, you often do not want anyone to see it while it is work in progress. Things are often broken, look ugly, ...etc.

Keeping humans off is not the only reason as well: you also need to keep out search engine crawlers, comment spam bots, email harvesters, Internet Archiver, ...etc.

At the same time, you want specific people to be able to access the site, such as the theme designer, fellow developers, someone from the client's company, ...etc. 

So here is a step by step guide on how to do that.

These instructions apply to Drupal and non-Drupal installation alike, as long as you are using the Apache web server. The instructions apply mostly to a UNIX/Linux system from the shell command line (e.g. via ssh to your web host server).

Create the password file

You need to create a password file. This password file must be created with the htpasswd command. Make sure you are in the directory that Drupal is installed  (the same directory that has the index.php and .htaccess files).

To use this command, you must say:

htpasswd -c .htpasswd user1

The -c option creates the file for the first time. guest is the ID you will enter the password for. 

You will be prompted for a password. Pick one that has both letters and numbers in it. 

Modify the .htaccess file

Next, in the .htaccess file, add the following lines. 

AuthType Basic
AuthName "Company XYZ Test Server"
AuthUserFile .htpasswd
Require valid-user 

 The AuthName will appear in the popup window in the browser when the user is prompted for a user name and password.

The AuthUserFile points to the file you created in the previous step.

Now you can pass on the user name and password to the client or others who need to see the site while it is under development. 

Further reading

More information can be found in the Apache documentation page on Authentication, Authorization and Access Control.