htaccess

## htaccess
# .htaccess file for root WordPress directory

# add this line if it's not already present in your .htaccess file
ErrorDocument 401 default

<Files "wp-login.php">
AuthName "WordPress Admin"
AuthUserFile "/path/to/passwd"
AuthType Basic
require valid-user
</Files>

## htaccess-2
# .htaccess file for wp-admin directory

# add this line if it's not already present in your .htaccess file
ErrorDocument 401 default

AuthName "WordPress Admin"
AuthUserFile "/path/to/passwd"
AuthType Basic
require valid-user

# allow anyone to access to admin-ajax.php
<Files "admin-ajax.php">
Allow from all
Satisfy Any
</Files>