LLM gateway security for routing, identity and cost control
An LLM gateway centralises keys, model routing and logs but becomes a critical trust point. Secure auth, tenants, retention, cache and fallback.
- AUTHOR
- Karol Rapacz / Penetration Tester (OSCP, PNPT)
- PUBLISHED
- 16 June 2026
- READING TIME
- 10 min read
- TOPIC
- AI Security
An LLM gateway centralises authentication, model routing, limits, caching and audit. It simplifies governance while becoming a critical point capable of reading organisation-wide prompts, tools and responses.
Identity and tenants
Every request carries user, workload, application and tenant identity. Do not trust client-set headers without token verification. Policy defines permitted models, region, budget and data classes.
Routing and fallback
Fallback can change retention, region, capability and safety policy. Treat it as a material change requiring explicit approval. Never route confidential prompts to a model not approved for that data class.
Logs and cache
Log metadata rather than full content by default. Prompts, tool arguments and results contain secrets. Encrypt caches, isolate tenants, limit TTL and include semantic caches in deletion workflows.
Resilience
Use per-identity rate limits, cost budgets, circuit breakers and retry-storm protection. Vault provider keys and rotate without downtime. An emergency route must preserve audit.
Test cross-tenant cache, header spoofing, model downgrade, fail-open behaviour and observability leaks. Connect controls with the AI model registry.
Gateway as a policy enforcement point
The gateway authenticates the application and user, resolves the tenant, then selects a provider and model. Never trust client headers without binding them to a verified identity. The policy covers permitted models, region, data classification, cost limit, tools and maximum context length.
Normalise provider APIs without hiding security semantics. If a required parameter or tool-call schema is unsupported, return a controlled error instead of silently dropping the safeguard. The model registry should record owner, version, evaluation results, regions and approved use cases.
Cache, logs and sensitive data
A cache key must include tenant, model, policy version and parameters affecting the answer. Sensitive workloads may require no cache. Encrypt data in transit and at rest, set retention and redact secrets before logging. Full prompts should not be a default observability metric.
Audit logs capture routing decision, policy version, identity, provider, model, usage and status without exposing provider keys. The gateway owns credentials; applications receive only the right to execute a defined request type.
Safe failure
Fallback is a new security decision. A replacement model must have a compatible region, support required controls and pass evaluation for the use case. Otherwise, deny the request or enter a restricted no-tools mode instead of choosing any available model.
Chaos tests should cover provider timeout, partial streaming, schema mismatch, retry storms and budget exhaustion. Verify that every path still writes an audit event, preserves tenant isolation and cannot bypass approval.
Tool calls and streaming
The gateway validates tool name and arguments before the executor. A provider adapter cannot silently change types, omit required fields or introduce unknown tools. Version every schema and keep a compatibility test.
A streaming response is incomplete until termination. Do not execute high-impact actions from a fragment that may later be cancelled or structurally changed. Limit buffer size, duration and concurrent streams, and account for cost after disconnects.
Operations and incident response
Dashboards should show provider errors, model distribution, tenant cost, policy denials, retries and fallback use. A sudden shift may indicate adapter failure, abuse or bad configuration.
Incident procedures need provider-key rotation, model disablement, region blocks and cache invalidation without stopping the whole platform. Emergency changes must retain a decision identifier and receive normal review afterwards.
Architecture review should also cover provider concentration and configuration export. Continuity does not mean automatic failover at any cost; it defines which features can be disabled when no safe replacement model is available.
Every new gateway client begins with the smallest profile and a separate limit. Expand permissions only after reviewing traffic, data, tools and failure scenarios.
Sources: OWASP Secure AI Model Ops, Anthropic LLM Gateway Configuration.
