Host-Service API Delegation¶
Delegating interface — instantiates Layer-Appropriate Capability Placement
Forwards a subsystem's capability request to the authoritative host service across a bounded, versioned API, so the host stays the single source of truth instead of being cloned locally.
Host-Service API Delegation is the plumbing by which an embedded subsystem, instead of implementing a capability itself, forwards the request across a defined boundary to the host service that authoritatively owns it — and returns the host's answer. Where a subsystem is tempted to keep its own copy of identity, storage, scheduling, or policy, delegation makes the host the single place that capability lives: the subsystem asks, the host decides and holds the state, and the subsystem consumes the result through a bounded, versioned interface. Its defining move is drawing an explicit delegated-authority boundary — a line that says this side merely requests; that side remains the source of truth — and recording every crossing, so the relationship stays legible rather than a tangle of hidden calls.
Example¶
A banking app needs to store a login token and a few secrets on the phone. The tempting local build is a small encrypted file with a hand-rolled key — a private credential store the app fully controls. Delegation takes the other path: the app calls the operating system's keychain/keystore API and lets the OS hold the secret, gate access behind the device's biometric prompt, and enforce hardware-backed protection the app could never reproduce. The app never sees the raw key material; it hands the OS a request ("store this; release it only after a face-match") and gets back a handle.
The authority boundary is explicit — the OS owns the secret and the security policy, the app owns only the request — and each store and retrieve is logged so a security reviewer can see exactly what was delegated. When the OS ships a new keychain API version, the app migrates against a documented contract rather than discovering a silent break. The alternative, a bespoke local vault, would have been a smaller, weaker clone of a capability the host already owns — the exact shadow-platform trap the archetype warns against.[1]
How it works¶
- Locate the authoritative owner. Identify the host service that already owns the capability and its state, rather than standing up a local equivalent.
- Forward across a bounded contract. The subsystem issues its request through a defined, versioned API surface — inputs, outputs, and errors specified — and treats the host's response as canonical.
- Hold the authority line. State and policy stay on the host side of the boundary; the subsystem keeps no shadow copy it would later have to reconcile.
- Record the crossing. Each delegated call is logged — what was asked, of which host version, with what outcome — so the dependency is observable and auditable.
Tuning parameters¶
- Boundary granularity — one coarse "do the whole thing" call versus many fine-grained ones. Coarse hides host detail and eases portability; fine-grained gives control but couples the subsystem tightly to the host's shape.
- Synchronicity — a blocking call versus a queued/async request. Async survives a slow host but complicates the subsystem; blocking is simple but inherits the host's latency.
- Result caching — whether responses may be cached locally, and for how long. Caching cuts load and latency but reintroduces a second copy that can go stale — the very duplication delegation exists to avoid.
- Failure posture — what the subsystem does when the host doesn't answer: fail closed, fail open, or fall back. Sets how far the delegation's reliability is bounded by the host's.
- Version pinning — whether the subsystem pins to a host API version or floats to latest. Pinning is stable but ages; floating stays current but can break on the host's schedule.
When it helps, and when it misleads¶
Its strength is that it keeps one source of truth: the capability lives where it is owned, the subsystem stays thin, and a whole class of reconciliation bugs and weaker-clone security holes never gets built. It is the constructive answer to "don't reimplement the host" — the mechanism you reach for the moment a subsystem is tempted to grow its own identity or storage layer.
Its failure modes come from the coupling it creates. A delegated capability is only as available as the host service, so an un-budgeted web of delegations can turn one host outage into a subsystem-wide stall; and a chatty, fine-grained contract can bind the subsystem so tightly to the host's internals that neither can change independently. The misuse to watch is delegation-in-name-only — forwarding to the host but then caching and mutating a local copy "for performance," quietly recreating the second source of truth. The discipline is to keep the authority boundary real (the host's answer is canonical; any local copy is at most a cache with an honest expiry) and to budget and observe the dependency rather than letting delegations accrete invisibly.
How it implements the components¶
Delegation fills the interface-and-authority side of the archetype — the components that let a subsystem use host capability rather than own it:
delegated_authority_boundary— the interface is the boundary: it fixes what the subsystem may request and reserves ownership of state and policy to the host.delegation_observability_record— every forwarded call is logged with its host version and outcome, making the dependency visible to operators and auditors.
It carries the ordinary, standing request path; it does not grant the rare out-of-band privilege that sits outside this surface (that's Privileged Host Escape Hatch), define the interface's version-compatibility contract (that's the sibling API Versioning), or publish the host's catalogue of capabilities (that's Capability Catalog).
Related¶
- Instantiates: Layer-Appropriate Capability Placement — it is the everyday means by which a subsystem uses host capability instead of rebuilding it.
- Consumes: the host's published interface and version contract — API Versioning governs whether that contract stays stable enough to delegate against.
- Sibling mechanisms: Privileged Host Escape Hatch · Host-Dependency Fallback Drill · Service Layer or API Facade · API Versioning · Adapter Layer · Capability Catalog
Editorial Notes¶
Form Classification¶
Form family: Control, Automation & Runtime
Rationale: At runtime the subsystem forwards capability requests through a bounded API to the authoritative host and uses the returned result without cloning host state.
Nearest alternative: Protocol, Workflow & Routine — The API defines an exchange protocol, but executable request delegation during operation is the primary form.
Review outcome: Adjudicated after independent review; high confidence.
Origin Attribution¶
Primary origin: Computer Science & Software Engineering
Origin pattern: Single lineage
Present-day reach: Specialized
Rationale: Delegating to a well-reviewed host capability rather than reimplementing it is a software-platform and API design principle.
Related originating lineages:
- Security Studies & Intelligence Analysis — Security engineering materially shaped the strongest version through the rule against rolling one's own cryptography and credential systems.
Review resolution: Both reviewers independently assign computer_science as the primary originating domain, so that shared primary is retained. Alternate domains are the union of reviewer-identified formative or independently originating lineages; later application settings alone are excluded. The evidence describes one principal historical lineage. Its defining controls and vocabulary remain bounded to a particular professional or technical practice. The encyclopedia entry generalizes the established mechanism without creating a new composite lineage.
Review outcome: Reconciled after independent review; high confidence.
Notes¶
Delegation and the Privileged Host Escape Hatch both let a subsystem use host power and are easily conflated. The difference is standing and breadth: delegation is the ordinary, durable, well-lit interface for capabilities the host means to expose; the escape hatch is a narrow, time-boxed exception for one it doesn't. If a subsystem is routinely reaching through an "escape hatch," that is a signal the capability should be promoted into a real delegated API.
References¶
[1] OWASP Foundation. “Cryptographic Storage Cheat Sheet”. OWASP Cheat Sheet Series (n.d.). Recommends provider-supplied key storage over ad hoc local storage because it centralizes management and rotation and offers stronger generation, compliance, and theft protections. registry ↩ Show verification details
Supported in partVerified against the work's full text
OWASP advises using the platform or cloud provider's key storage over keys in config files, citing central management, compliance and harder theft.
“Where available, the secure storage mechanisms provided by the operating system, framework or cloud service provider should be used.”