feat: Validate LiteLLM Virtual Key format (#14428)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: ishaan <ishaan@berri.ai>

litellm/proxy/management_endpoints/key_management_endpoints.py

@@ -551,6 +551,15 @@ async def _common_key_generation_helper(  # noqa: PLR0915
         prisma_client=prisma_client,
     )
 
+    # Validate user-provided key format
+    if data.key is not None and not data.key.startswith("sk-"):
+        raise HTTPException(
+            status_code=400,
+            detail={
+                "error": f"Invalid key format. LiteLLM Virtual Key must start with 'sk-'. Received: {data.key}"
+            }
+        )
+
     response = await generate_key_helper_fn(
         request_type="key", **data_json, table_name="key"
     )