Design Credit-Card Authorization, Limit Decisions, and Reporting

Design a backend for a credit card product. It must support: cardholder login and session management; transaction authorization that considers fraud signals; spending summary and transaction history views; decisions about increasing or decreasing a cardholder’s credit limit; monthly statement generation. All mutating endpoints must be idempotent: if a request is retried or duplicated, the system should apply the change at most once and return a consistent response. The…