feat: service token introduction

core/auth/fetch_sub.py

@@ -0,0 +1,17 @@
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from db.models import User
+from repositories.users import UserRepository
+from schemas.jwt import ServiceJWTPayload
+
+
+async def fetch_subject_from_service(
+    payload: ServiceJWTPayload, session: AsyncSession
+) -> User | None:
+    repo = UserRepository(session)
+
+    if payload.acting_as.startswith("telegram:"):
+        telegram_id = int(payload.acting_as.split("telegram:")[1])
+        return await repo.get_user_by_telegram_id(telegram_id)
+
+    return