ExpirySignal — Spec Sheet

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Inputs

• Entity identifier such as user, account, token, scope, or custom key
• Expiry timestamp or expiry window written by your system
• Optional context identifier such as scope, feature, or environment
• Time source used at read time
• Optional cause code or renewable metadata written by your system

Outputs

• expired boolean
• expires_at timestamp
• cause_code if present
• renewable boolean if present
• Read-time JSON response for application evaluation

Renewable field

• renewable is operator-provided metadata stored alongside the expiry record.
• It is not computed from rules.
• It does not grant permission to renew.
• If renewal is allowed, your application must implement the renewal workflow and write a new expiry record explicitly.

Guarantees

• Returns stored expiry state as of read time
• Compares stored expiry state against the configured time source
• Does not mutate state on read
• Does not execute side effects on read

Non-guarantees

• Clock correctness or clock synchronization
• Timeliness of expiry writes
• Consistency across distributed systems
• Authorization correctness
• Session invalidation, token revocation, or renewal correctness
• Security, safety, or compliance outcomes

Invariants

• Not expired is not authorized
• Expiry state is not permission
• Absence of an expiry record is not permission
• Renewable metadata is not renewal authorization
• Returned state is application-evaluated

Failure modes

• Clock skew or time mismatch → readers can disagree across deployments
• Missing or delayed expiry write → reads can be wrong
• Identifier mismatch → wrong entity state returned
• Partial writes or database inconsistency → stale or incorrect reads
• Network or database failure → reads can fail or time out
• Application treats “not expired” as automatic permission

Performance characteristics

• Read latency: typically a PostgreSQL point lookup plus time comparison
• Concurrency: limited by your PostgreSQL connection pool and indexes
• Scheduling: none
• Background execution: none
• Time source: your clock; correctness and synchronization are your responsibility

Out of scope

• Session invalidation
• Token revocation
• Request blocking
• Background execution
• Policy definition
• Automatic enforcement
• Renewal workflow execution

Implementation details

• Language: TypeScript (Node.js)
• Interface: HTTP or embedded application call depending on deployment
• Database: PostgreSQL
• Deployment: self-hosted service or embedded local component