How do i set basic authentication in http header php?

It is possible to use the header[] function to send an "Authentication Required" message to the client browser causing it to pop up a Username/Password input window. Once the user has filled in a username and a password, the URL containing the PHP script will be called again with the predefined variables PHP_AUTH_USER, PHP_AUTH_PW, and AUTH_TYPE set to the user name, password and authentication type respectively. These predefined variables are found in the $_SERVER array. Only "Basic" and "Digest" authentication methods are supported. See the header[] function for more information.

An example script fragment which would force client authentication on a page is as follows:

Example #1 Basic HTTP Authentication example