Keycloak

Keycloak (Wikipedia) is identity and access management software, and can serve as an authentication server for applications (providing support for OpenID Connect, OAuth 2.0, and SAML.)

Keycloak is...

• covered in the NixOS manual
• packaged for Nix
• available as a Nix service
• written in Java
• maintained by Red Hat

Troubleshooting

Installing on system without X11

If, when you perform:

nixos-rebuild switch

... you encounter errors like:

building Nix...

...

checking for CAIRO_BACKEND... no
configure: error: Package requirements (cairo-xlib >= 1.6) were not met:

No package 'cairo-xlib' found

...

error: build of '/nix/store/vfz...2a0-nixos-system-nixos-21.11pre322478.e4ef597edfd.drv' failed

... it would be because the package expects X11 to be installed. The environment.noXlibs NixOS option will specify to not require the X11 libraries:

/etc/nixos/configuration.nix

{ config, pkgs, ... }:

{
  environment.noXlibs = false;
}