Configure SCP access for login without a local account

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http://unix.stackexchange.com – Can I set up accounts that can do SCP that are NOT local users (i.e. users with an entry in passwd). I've tried googling for SCP "without PAM authentication" or alternative authenication for sshd but I have not yet found anything that I can use. In other words: How can I configure SCP access on my Debian linux machine without having to create a new local account/local user. Doing this would be useful example in the case of a webhost with several VirtualHost entries in httpd.conf allowing people to securely upload their website assets without the admin having to create an account and setup SS (HowTos)