However if you only have FTP access and not DNS/Cpanel access then the following tweak to your htaccess will be useful:
[change subdir to the name of your password-protected sub directory]
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteBase /
RewriteCond %{REQUEST_URI} ^/subdir/ [OR]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
A more complete Wordpress htaccess file is as follows, forcing browser caching, enabling server-based GZIP compression, redirect from www. to the primary domain name, the Wordpress upload fix, and then the standard SEF URL Wordpress modrewrite code with access to the password-protected subdir included.
# Set Expire Date
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/html "access plus 1 seconds"
ExpiresByType image/gif "access plus 2 years"
ExpiresByType image/doc "access plus 1 weeks"
ExpiresByType image/pdf "access plus 1 weeks"
ExpiresByType image/zip "access plus 1 weeks"
ExpiresByType image/jpeg "access plus 2 years"
ExpiresByType image/png "access plus 2 years"
ExpiresByType text/css "access plus 2 years"
ExpiresByType text/javascript "access plus 2 years"
ExpiresByType application/x-javascript "access plus 2 years"
</IfModule>
# GZip if possible
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTP:accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME} !^.+\.gz$
RewriteCond %{REQUEST_FILENAME}.gz -f
RewriteRule ^(.+) $1.gz [L]
# If subdomain www exists, remove it first
RewriteCond %{HTTP_HOST} ^www\.([^\.]+\.[^\.]+)$ [NC]
RewriteRule ^(.*)$ [
%1...] [R=301,L]
# If requested resource does not exist as a file
RewriteCond %{REQUEST_FILENAME} !-f
# and does not end with a period followed by a filetype
RewriteCond %{REQUEST_URI} !..+$
# and does not end with a slash
RewriteCond %{REQUEST_URI} !/$
# then add a trailing slash and redirect
RewriteRule (.*) $1/ [R=301,L]
</IfModule>
# WordPress upload fix
<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteBase /
RewriteCond %{REQUEST_URI} ^/subdir/ [OR]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
