Is it possible to display my window over a Windows logon screen?

Question

I'm writing a service/user-mode application that may send the system into sleep after a certain customizable period of inactivity. The user-mode process may require to display a user message/warning before performing a power operation. This works great if a user is logged in, but if the workstation is locked, a user sees a display like this:

So I'm curious if it is possible to display my own window (overlay) above such a logon screen?

Ice

Interesting question. I know precious little about Windows internals, but my gut instinct is that this won't be possible, due to potential security implications (faking a login form). – Hyperbola

There are ways using Windows Interactive Logon Architecture. General idea can be seen here - #12498519 – Theocracy

Or possibly this question. – Thermos

Thank you. Everyone seems to caution against it. Can someone give an example of why is it a security concern and how can it be exploited? – Ice

@Ice if one was feeling evil, one could write their own "login window" that would look and act just like the real one, except that it would also email the user's typed-in username and password to evilhackers.com for later (ab)use. – Crossquestion

because anything that can draw over the login screen can fake it to take the user's password. That's why windows server have always required users to press ctrl+alt+del to login since nothing can catch that key combinations. So if someone runs a program, for example a screen saver, that looks like a login screen cannot have focus after pressing the key – Marchetti

Answer 1

The only supported API for this, since Vista, is the credential provider. The documentation can be found over on MSDN.

Apocalyptic

Answer 2

I found this post that might be exactly what I need. I'll post later when I try it out...

Ice

The link is down. Fortunately the wayback machine still has it: web.archive.org/web/20150505112059/http://calebdelnay.com/blog/… – Kakapo