nixos/keycloak: Use LoadCredential to load secrets

Use systemd's LoadCredential mechanism to make the secret files
available to the service.

This gets rid of the privileged part of the ExecPreStart script which
only served to copy these files and assign the correct
permissions. There's been issues with this approach when used in
combination with DynamicUser, where sometimes the user isn't created
before the ExecPreStart script runs, causing the error

install: invalid user ‘keycloak’

This should fix that issue.

Unfortunately, all of the ExecPreStart script had to be moved to
ExecStart, since credentials aren't provided to ExecPreStart. See
https://github.com/systemd/systemd/issues/19604.

nixos/modules/services/web-apps/keycloak.nix

@@ -735,52 +735,16 @@ in
               JBOSS_MODULEPATH = "${cfg.package}/modules";
             };
             serviceConfig = {
-              ExecStartPre = let
+              LoadCredential = [
-                startPreFullPrivileges = ''
+                "db_password:${cfg.database.passwordFile}"
-                  set -o errexit -o pipefail -o nounset -o errtrace
+              ] ++ lib.optionals (cfg.sslCertificate != null && cfg.sslCertificateKey != null) [
-                  shopt -s inherit_errexit
+                "ssl_cert:${cfg.sslCertificate}"
-
+                "ssl_key:${cfg.sslCertificateKey}"
-                  umask u=rwx,g=,o=
-
-                  install -T -m 0400 -o keycloak -g keycloak '${cfg.database.passwordFile}' /run/keycloak/secrets/db_password
-                '' + lib.optionalString (cfg.sslCertificate != null && cfg.sslCertificateKey != null) ''
-                  install -T -m 0400 -o keycloak -g keycloak '${cfg.sslCertificate}' /run/keycloak/secrets/ssl_cert
-                  install -T -m 0400 -o keycloak -g keycloak '${cfg.sslCertificateKey}' /run/keycloak/secrets/ssl_key
-                '';
-                startPre = ''
-                  set -o errexit -o pipefail -o nounset -o errtrace
-                  shopt -s inherit_errexit
-
-                  umask u=rwx,g=,o=
-
-                  install -m 0600 ${cfg.package}/standalone/configuration/*.properties /run/keycloak/configuration
-                  install -T -m 0600 ${keycloakConfig} /run/keycloak/configuration/standalone.xml
-
-                  replace-secret '@db-password@' '/run/keycloak/secrets/db_password' /run/keycloak/configuration/standalone.xml
-
-                  export JAVA_OPTS=-Djboss.server.config.user.dir=/run/keycloak/configuration
-                  add-user-keycloak.sh -u admin -p '${cfg.initialAdminPassword}'
-                '' + lib.optionalString (cfg.sslCertificate != null && cfg.sslCertificateKey != null) ''
-                  pushd /run/keycloak/ssl/
-                  cat /run/keycloak/secrets/ssl_cert <(echo) \
-                      /run/keycloak/secrets/ssl_key <(echo) \
-                      /etc/ssl/certs/ca-certificates.crt \
-                      > allcerts.pem
-                  openssl pkcs12 -export -in /run/keycloak/secrets/ssl_cert -inkey /run/keycloak/secrets/ssl_key -chain \
-                                 -name "${cfg.frontendUrl}" -out certificate_private_key_bundle.p12 \
-                                 -CAfile allcerts.pem -passout pass:notsosecretpassword
-                  popd
-                '';
-              in [
-                "+${pkgs.writeShellScript "keycloak-start-pre-full-privileges" startPreFullPrivileges}"
-                "${pkgs.writeShellScript "keycloak-start-pre" startPre}"
               ];
-              ExecStart = "${cfg.package}/bin/standalone.sh";
               User = "keycloak";
               Group = "keycloak";
               DynamicUser = true;
               RuntimeDirectory = map (p: "keycloak/" + p) [
-                "secrets"
                 "configuration"
                 "deployments"
                 "data"
@@ -792,6 +756,32 @@ in
               LogsDirectory = "keycloak";
               AmbientCapabilities = "CAP_NET_BIND_SERVICE";
             };
+            script = ''
+              set -o errexit -o pipefail -o nounset -o errtrace
+              shopt -s inherit_errexit
+
+              umask u=rwx,g=,o=
+
+              install -m 0600 ${cfg.package}/standalone/configuration/*.properties /run/keycloak/configuration
+              install -T -m 0600 ${keycloakConfig} /run/keycloak/configuration/standalone.xml
+
+              replace-secret '@db-password@' "$CREDENTIALS_DIRECTORY/db_password" /run/keycloak/configuration/standalone.xml
+
+              export JAVA_OPTS=-Djboss.server.config.user.dir=/run/keycloak/configuration
+              add-user-keycloak.sh -u admin -p '${cfg.initialAdminPassword}'
+            '' + lib.optionalString (cfg.sslCertificate != null && cfg.sslCertificateKey != null) ''
+              pushd /run/keycloak/ssl/
+              cat "$CREDENTIALS_DIRECTORY/ssl_cert" <(echo) \
+                  "$CREDENTIALS_DIRECTORY/ssl_key" <(echo) \
+                  /etc/ssl/certs/ca-certificates.crt \
+                  > allcerts.pem
+              openssl pkcs12 -export -in "$CREDENTIALS_DIRECTORY/ssl_cert" -inkey "$CREDENTIALS_DIRECTORY/ssl_key" -chain \
+                             -name "${cfg.frontendUrl}" -out certificate_private_key_bundle.p12 \
+                             -CAfile allcerts.pem -passout pass:notsosecretpassword
+              popd
+            '' + ''
+              ${cfg.package}/bin/standalone.sh
+            '';
           };
 
         services.postgresql.enable = lib.mkDefault createLocalPostgreSQL;