feat: service token introduction

repositories/service_signatures.py

@@ -0,0 +1,11 @@
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from db.models.service_signatures import ServiceSignature
+
+
+async def get_active_signature_by_kid(session: AsyncSession, kid: str) -> ServiceSignature | None:
+    stmt = select(ServiceSignature).where(ServiceSignature.kid == kid)
+    r = await session.execute(stmt)
+
+    return r.scalar_one_or_none()