feat: Add audit logging (#38189)

Co-authored-by: bircni <bircni@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/common/auth.go

@@ -5,6 +5,7 @@ package common
 
 import (
 	user_model "gitea.dev/models/user"
+	"gitea.dev/modules/log"
 	"gitea.dev/modules/web/middleware"
 	auth_service "gitea.dev/services/auth"
 	"gitea.dev/services/context"
@@ -30,6 +31,18 @@ func AuthShared(ctx *context.Base, sessionStore auth_service.SessionStore, authM
 		ctx.Data[middleware.ContextDataKeySignedUser] = ar.Doer
 		ctx.Data["SignedUserID"] = ar.Doer.ID
 		ctx.Data["IsAdmin"] = ar.Doer.IsAdmin
+
+		if sessionStore != nil {
+			if uid := auth_service.ImpersonatorUserID(sessionStore); uid != 0 {
+				impersonator, err := user_model.GetUserByID(ctx, uid)
+				if err != nil {
+					// the session stays usable, but audit events must not silently lose the admin behind it
+					log.Error("Unable to resolve impersonator %d: %v", uid, err)
+				} else {
+					ctx.Data[middleware.ContextDataKeyImpersonator] = impersonator
+				}
+			}
+		}
 	} else {
 		ctx.Data["SignedUserID"] = int64(0)
 	}