Usage

{
 inputs = {
 # ...
 authologin.url = "git+https://codeberg.org/ollijh/authologin";
 authologin.inputs.nixpkgs.follows = "nixpkgs";
 # ...
 };
 outputs = { nixpkgs, authologin, ... }: {
 nixosConfigurations.joes-desktop = nixpkgs.lib.nixosSystem {
 # ...
 modules = [
 # ...
 authologin.nixosModules.default
 ({lib, ...}: {
 services.authologin = {
 enable = true;
 user = "joe"; # Replace with your username.
 command = lib.getExe config.programs.sway.package; # To start Sway, for example.
 };
 })
 ];
 };
 };
}

Will try to use your disk encryption password to authenticate and open GNOME keyring if your root disk is encrypted.

Note that the PAM configuration is rather fixed (see flake.nix), so if you need to alter it you have to replace the whole thing.