Should we add rate limiting to our Open Banking API?

When it comes to creating PSD2 APIs for banks or any other APIs for that matter, implementing effective rate limiting is crucial to ensure the security, stability, and fair usage of the API.

Here are some best practices for rate limiting in the context of PSD2 APIs:

  • Define Rate Limiting Policies: Clearly define and document your rate limiting policies, including the number of requests allowed per time interval (e.g., per second, minute, or hour). Make this information readily available to developers in your API documentation.
  • Use Token-Based Authentication: Implement token-based authentication for API access. This allows you to tie rate limits to specific API keys or OAuth tokens, ensuring that individual developers or applications are rate-limited independently.
  • Granularity: Consider setting different rate limits for different types of endpoints or operations within your API. Not all API endpoints may have the same sensitivity or usage patterns, so tailor rate limits accordingly.
  • Prioritize PSD2-Specific Endpoints: Given the specific requirements of PSD2, prioritize endpoints related to essential functions like payment initiation and account information access. Ensure that these endpoints have appropriate rate limits to handle expected traffic.
  • Per-Consent Rate Limits: Implement rate limiting on a per-consent basis. Each consent given by the customer for accessing their account information should have its rate limit. This prevents overuse of the API by individual consents.
  • Consent Expiry Handling: When a consent expires or is revoked, promptly disable access to the associated API resources. This ensures that no further requests can be made with an invalidated consent.
  • Rate Limits Based on Consent Type: Consider different rate limits for different types of AIS requests. For example, basic account information retrieval may have a higher rate limit than more sensitive transactions like transaction history access or balance inquiries.
  • Dynamic Rate Limiting: Implement dynamic rate limiting based on the load and health of your API infrastructure. For example, during peak traffic times, you might temporarily tighten rate limits to prevent overloading.
  • Error Handling: When a client exceeds their rate limit, provide clear and informative error messages. Include details on the rate limit, when it will reset, and guidance on how to avoid rate limiting in the future.
  • Rate Limit Headers: Include rate limit information in the response headers, such as "X-RateLimit-Limit," "X-RateLimit-Remaining," and "X-RateLimit-Reset." This helps developers and clients keep track of their usage.
  • Monitoring and Analytics: Implement monitoring and analytics to track API usage patterns and identify potential abuse or abnormal behaviour. Tools like API gateways and API management platforms can provide valuable insights.
  • Rate Limiting Exemptions: Consider allowing for exemptions or higher rate limits for trusted or premium users, provided that you can identify and authenticate them appropriately.
  • Scalability: Design your AIS API infrastructure to be scalable to handle increased traffic during peak periods. This ensures that the API remains available and responsive under high loads.
  • Regular Review and Adjustments: Periodically review your rate limiting policies and adjust them as needed based on changing usage patterns and the evolving threat landscape. Flexibility is key.
  • Education and Outreach: Provide educational resources and support for developers to help them understand and work within the rate limits effectively. This can include documentation, FAQs, and developer forums.
  • Compliance with PSD2 Regulations: Ensure that your rate limiting policies align with the PSD2 regulatory requirements for security, availability, and performance of APIs.

Remember that effective rate limiting is not just about security, but also about delivering a reliable and positive developer experience. It's a balancing act between preventing abuse and allowing legitimate usage. Regularly assessing and fine-tuning your rate limiting strategies will help you achieve this balance.


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