The gdm-devel package contains headers and other files needed to build custom greeters.
acquired package info from repodata DB: repodata/f0b2606f1dc0294014b17bb8ea9231f0129611b4c9610b9db40f82da2b1f63da-primary.sqlite.bz2
GDM, the GNOME Display Manager, handles authentication-related backend functionality for logging in a user and unlocking the user's session after it's been locked. GDM also provides functionality for initiating user-switching, so more than one user can be logged in at the same time. It handles graphical session registration with the system for both local and remote sessions (in the latter case, via the XDMCP protocol). In cases where the session doesn't provide it's own display server, GDM can start the display server on behalf of the session.