Auth: Introduce pre-logout hooks + add GCOM LogoutHook (#88475)

* Introduce preLogoutHooks in authn service

* Add gcom_logout_hook

* Config the api token from the Grafana config file

* Simplify

* Add tests for logout hook

* Clean up

* Update

* Address PR comment

* Fix

pkg/services/auth/gcomsso/gcom_logout_hook.go

@@ -0,0 +1,65 @@
+package gcomsso
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"net/http"
+
+	"github.com/grafana/grafana/pkg/models/usertoken"
+	"github.com/grafana/grafana/pkg/services/auth/identity"
+	"github.com/grafana/grafana/pkg/setting"
+)
+
+type gcomLogoutRequest struct {
+	Token     string `json:"idToken"`
+	SessionID string `json:"sessionId"`
+}
+
+type GComSSOService struct {
+	cfg    *setting.Cfg
+	logger *slog.Logger
+}
+
+func ProvideGComSSOService(cfg *setting.Cfg) *GComSSOService {
+	return &GComSSOService{
+		cfg:    cfg,
+		logger: slog.Default().With("logger", "gcomsso-service"),
+	}
+}
+
+func (s *GComSSOService) LogoutHook(ctx context.Context, user identity.Requester, sessionToken *usertoken.UserToken) error {
+	s.logger.Debug("Logging out from Grafana.com", "user", user.GetID(), "session", sessionToken.Id)
+	data, err := json.Marshal(&gcomLogoutRequest{
+		Token:     user.GetIDToken(),
+		SessionID: fmt.Sprint(sessionToken.Id),
+	})
+	if err != nil {
+		s.logger.Error("failed to marshal request", "error", err)
+		return err
+	}
+
+	hReq, err := http.NewRequestWithContext(ctx, http.MethodPost, s.cfg.GrafanaComURL+"/api/logout/grafana/sso", bytes.NewReader(data))
+	if err != nil {
+		return err
+	}
+	hReq.Header.Add("Content-Type", "application/json")
+	hReq.Header.Add("Authorization", "Bearer "+s.cfg.GrafanaComSSOAPIToken)
+
+	c := http.DefaultClient
+	resp, err := c.Do(hReq)
+	if err != nil {
+		s.logger.Error("failed to send request", "error", err)
+		return err
+	}
+	// nolint: errcheck
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusNoContent {
+		return fmt.Errorf("failed to logout from grafana com: %d", resp.StatusCode)
+	}
+
+	return nil
+}