I'm working on a website in which I -as an admin- need to be able to access a PHP script that no one else can. Building a whole login system with accounts would be overkill in this case, as I would be the only one using it.
So my question is, how can I create a very basic yet secure authentication system?
Given that I have an Apache HTTP Server, can I use the .htaccess file to forbid access to certain PHP files and ask for a certain combination of username/password?
Yes you can use Basic Auth with .htaccess see: http://httpd.apache.org/docs/current/howto/auth.html
And yes, you can define that only 1 file is asking for Username/Password.
Little example e.g. for file "secure.php"
<Files secure.php>
AuthType basic
AuthName "Need Login"
AuthUserFile /path/to/.htusers
Require valid-user
</Files>
Yes, you can, using .htaccess files and htpasswd command.
Try to search with ".htaccess authorization" in Google.
Setting up an .htaccess Protected Directory or file.