Form data exceeding 1MB causes HTTP 400 errors since Starlette 0.40.0

Since Starlette 0.40.0, form parameters exceeding the default 1024KB (1MB) limit trigger HTTP 400 errors with message 'Part exceeded maximum size of 1024KB.' This is due to the new max_part_size attribute in MultiPartParser introduced to resolve a security vulnerability.

Override max_part_size by intercepting requests with middleware and calling request.form() with custom max_part_size parameter. Example: await request.form(max_part_size=50*1024*1024) for 50MB limit. Alternatively, create a custom request class or use a Depends function that returns FormData with custom limits. Avoid using BaseHTTPMiddleware as it causes form data loss.