gatekeep

The soul selects her own society, Then shuts the door;

— Emily Dickinson, "Exclusion" (1890)

gatekeep 3.0 is a code-first authorization engine for Rust. Policies are ordinary Rust values, a pure deterministic core evaluates them, and every decision carries the reasons that produced it.

The project keeps policy in Rust. A policy is an ordinary, typed value that can be composed, tested, serialized, and hashed alongside application code. An external policy language can be the right shared contract across services or teams; gatekeep targets the case where Rust owns the model and the policy should remain visible to the compiler and ordinary tests.

Documentation

• docs/ — guides and reference for integrators
• docs.rs/gatekeep — core crate API
• Adapter crates: gatekeep-axum, gatekeep-fluent, gatekeep-keepsake, gatekeep-sqlx

Read Combining permit outcomes before designing graded access such as redacted/full records or scope unions.

A policy

use gatekeep::{
    condition, evaluate, policy, DecisiveClause, Effect, Fact, GatekeepResult, KnownFacts,
    Lattice, ReasonCode, StaticFactId,
};

// Outcome grade: how much of a record the caller may read.
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, serde::Serialize)]
enum ReadAccess {
    Redacted,
    Full,
}

impl Lattice for ReadAccess {
    fn meet(&self, other: &Self) -> Self { (*self).min(*other) }
    fn join(&self, other: &Self) -> Self { (*self).max(*other) }
    fn top() -> Self { Self::Full }
    fn bottom() -> Self { Self::Redacted }
}

// A fact the application resolves before evaluation.
struct CaseOwner;

impl Fact for CaseOwner {
    const ID: StaticFactId = StaticFactId::new("case_owner");
}

fn read_access() -> GatekeepResult<()> {
    // "The case owner may read the full record."
    let owner_full_read = policy::grant(ReadAccess::Full, condition::has::<CaseOwner>())
        .try_labeled("owner_full_read")?
        .try_reason("not_case_owner")?;

    // The owner is permitted, with the granted grade carried on the effect.
    let permitted = evaluate(&owner_full_read, &KnownFacts::new().with_present::<CaseOwner>());
    assert_eq!(permitted.effect, Effect::Permit(ReadAccess::Full));

    // A non-owner is denied, and the decision explains itself instead of
    // returning a bare "no": the facts that were missing and a stable reason
    // code your UI or audit log can map to a message.
    let denied = evaluate(&owner_full_read, &KnownFacts::new());
    assert_eq!(denied.effect, Effect::Deny);
    if let DecisiveClause::Deny { reason, unsatisfied, .. } = &denied.trace.decisive {
        assert_eq!(reason.as_ref().map(ReasonCode::as_str), Some("not_case_owner"));
        assert_eq!(unsatisfied.len(), 1); // the missing case_owner fact
    }

    Ok(())
}

The application resolves facts before evaluation. Gatekeep is an in-process authorization boundary; it does not authenticate requests, manage sessions or tenancy, provide a network policy service, or define a separate policy DSL. Those concerns remain with application code or a crate built for them.

Tenant binding is explicit: the application verifies identity and tenant membership, then constructs a bounded binding that Gatekeep checks for match and freshness. Gatekeep does not verify OIDC/JWT tokens or execute obligations.

Each policy is inspectable data. Gatekeep can serialize and hash it, explain a decision, and answer "which resources can this principal reach?", not just "may this principal reach this one?".

Partial evaluation reuses the same policy value with PartialFacts: mark request-known facts as present or absent, leave resource-level facts unknown, then lower the residual policy in an application-owned adapter. For SQL-backed list queries, gatekeep-sqlx maps residual facts to trusted row predicates and appends a lowered filter and grade projection to a sqlx::QueryBuilder. Postgres is the default backend; SQLite and MySQL are available behind feature flags.

For durable decision audit, configure an application-owned absolute source URI and a Dovecote-backed AuditSink. gatekeep-sqlx provides PgDovecoteAudit, SqliteDovecoteAudit, and MySqlDovecoteAudit. Install the selected Dovecote schema, call the adapter's check_schema, then pass the sink to Gatekeeper::new(resolver, audit). The Axum adapter awaits the audit write before returning permit or deny. Each decision becomes one complete JSON event and one pending Dovecote delivery; Gatekeep does not maintain a parallel audit table or outbox.

The compile-checked axum-durable-audit example imports gatekeep_axum::Gatekeeper, obtains a real application-owned FactResolver, checks the Dovecote schema, and constructs Gatekeeper::new(resolver, PgDovecoteAudit). Use that example as the canonical setup when wiring a service.

Use Dovecote's matching migration under its migrations/ directory. Export workers claim and page Dovecote deliveries; Gatekeep's typed AuditEntry is the event payload and Dovecote owns delivery lifecycle and retry state. The old gatekeep-sqlx audit migrations remain in this repository as immutable v1 upgrade artifacts only; 3.0 has no runtime API for their tables.

For the lowering walkthrough, see the gatekeep-sqlx docs on docs.rs and the axum-authorized-list example.

License

Licensed under either of:

• Apache License, Version 2.0
• MIT license

at your option.