APIs have become the backbone of modern software architecture, powering mobile applications, microservices communication, third-party integrations, and IoT ecosystems. This ubiquity makes APIs a prime target for attackers—Gartner projected that APIs would become the most-attacked surface area by 2025. Despite this, API security often lags behind traditional web application security. At Nexis Limited, we design and implement APIs with security as a foundational requirement, not an afterthought.

The OWASP API Security Top 10

The OWASP API Security Top 10 (2023 edition) identifies the most critical API-specific risks. The top entries are: Broken Object Level Authorization (BOLA), where attackers manipulate object IDs in API requests to access other users' resources; Broken Authentication, covering weak token generation, missing token validation, and inadequate credential management; and Broken Object Property Level Authorization, where APIs expose sensitive object properties in responses or allow mass assignment of protected fields. Understanding these risks is the first step toward building secure APIs.

Authentication and Authorization

API authentication must be robust and stateless. OAuth 2.0 with OpenID Connect (OIDC) is the standard for user-facing APIs, providing scoped access tokens with defined lifetimes. For service-to-service communication, mutual TLS (mTLS) or OAuth 2.0 client credentials flow provides strong machine identity verification. JWT tokens should use asymmetric signing algorithms (RS256 or ES256)—never HS256 with shared secrets in distributed systems. Token validation must verify signature, expiration, issuer, audience, and scopes on every request. Implement token refresh rotation to limit the window of exposure from stolen tokens.

Fine-Grained Authorization

Authentication answers "who are you?" while authorization answers "what can you do?" Every API endpoint must enforce authorization checks at the object level—verifying that the authenticated user has permission to access the specific resource they're requesting. This prevents BOLA vulnerabilities, which are the number one API security risk. Implement authorization middleware that validates permissions before any business logic executes. For complex permission models, consider policy engines like Open Policy Agent (OPA) that externalize authorization logic into declarative policies.

Rate Limiting and Throttling

Rate limiting protects APIs from abuse, brute-force attacks, and denial-of-service conditions. Implement rate limits at multiple levels: global limits per API gateway, per-user limits based on authentication tokens, and per-endpoint limits for sensitive operations like authentication or password reset. Use token bucket or sliding window algorithms for smooth rate enforcement. Response headers should communicate rate limit status (X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset) so clients can adapt their behavior. For advanced scenarios, implement adaptive rate limiting that adjusts thresholds based on real-time abuse detection signals.

Input Validation and Output Encoding

Every API input must be validated against a strict schema. OpenAPI/Swagger specifications define expected request formats—use schema validation middleware to reject requests that don't conform. Validate data types, string lengths, numeric ranges, allowed values, and required fields. Reject unexpected fields to prevent mass assignment attacks. For output, never return more data than the client needs—implement response filtering to strip internal fields, database IDs, and sensitive attributes. GraphQL APIs require particular attention, as overly permissive schemas can enable deep query attacks and information disclosure through introspection.

API Gateway and Monitoring

An API gateway serves as the centralized enforcement point for cross-cutting security concerns: authentication, rate limiting, request/response transformation, and logging. Solutions like Kong, AWS API Gateway, or Azure API Management provide these capabilities out of the box. Comprehensive API logging—capturing request metadata, authentication context, response codes, and latency—feeds into SIEM platforms for security monitoring. Alert on anomalous patterns: sudden spikes in 401/403 responses, unusual request volumes from single clients, or sequential enumeration of resource identifiers.

As Bangladeshi businesses increasingly rely on API-driven architectures for fintech, e-commerce, and digital services, securing these interfaces is critical. A single API vulnerability can expose entire databases, enable unauthorized transactions, or compromise downstream systems. Contact us to review your API security posture and implement industry-standard protections across your digital infrastructure.