alktls/docs/architecture/overview.md

status, last_updated

status	last_updated
draft	2026-09-10

alktls — Overview

Purpose

alktls is the TLS layer of the alk* stack: shared TLS setup types — server and client rustls configs, cert resolvers, verifiers, and ACME state-machine wiring — transport-agnostic and shareable across transports. It is the extraction of the TLS handling from alknet (crates/alknet-tls + the identity/credential/fingerprint types in crates/alknet-core), and it is the TLS crate the alknet rewrite consumes.

The crate owns config construction: given an identity and an ALPN list, produce a rustls::ServerConfig or rustls::ClientConfig, and hand it to whichever transport wrapper the deployment runs. It does not dial, accept, dispatch, or resolve peer identities — those are the dial seam's, the accept loop's, and the auth layer's jobs (alknet ADR-083/089; the scope boundary in ADR-001).

Terminology. The assembly layer is the deployment binary that builds the TlsServerConfigs / TlsClientConfigs, builds the transports from them, and wires the results together (alknet ADR-014's term — in practice, the hub/worker/endpoint binary). The dial seam is the outbound connection point the assembly layer (or a client crate) consumes; the accept loop is the inbound counterpart. alktls is the cert provider for both, never the loops themselves.

The transport picture

A deployment (endpoint / hub) assembles a subset of three transports; alktls serves the first two directly and feeds the third a key:

Transport	Stack	What alktls provides
TCP+TLS	tokio-rustls	TlsServerConfig::for_tcp_tls() → TlsAcceptor (feature tcp); TlsClientConfig::into_rustls_config() → TlsConnector (ungated)
QUIC	noq (iroh's extracted quinn fork)	for_noq() on both configs (feature noq)
iroh	iroh's own TLS	nothing — Ed25519SecretKey 32-byte access feeds iroh_base::SecretKey (key-not-config)

One identity, N transports: the inner rustls config is Clone (Arc-shared resolvers); one TlsServerConfig feeds every transport an endpoint runs. One ACME state machine per domain, shared across transports — duplicate orders risk Let's Encrypt rate limits and cert-cache divergence (ADR-001).

What the crate is

The public API surface (ADR-004, ADR-005):

• TlsServerConfig — built once from a TlsIdentity + ALPN list; accessors for_noq(), for_tcp_tls(), rustls_config(). Not Clone (holds the ACME task's JoinHandle); share via Arc.
• TlsClientConfig — built per dial from ConnectionCredentials + ALPN; accessors for_noq(), into_rustls_config().
• TlsError — the ADR-088 six-variant #[non_exhaustive] config-construction error type (ADR-002).
• Identity types — TlsIdentity (X509 / RawKey / SelfSigned / Acme), Ed25519SecretKey, AcmeDirectory (ADR-005).
• Credential bundle — ConnectionCredentials, RemoteIdentity (ADR-005); drives the verifier selection matrix (alknet ADR-034).
• Fingerprint helpers — fingerprint_from_cert_der, extract_ed25519_raw_key_from_spki (ADR-005); normalized ed25519:<hex> / SHA256:<hex> formats.

Design Decisions

All design decisions are documented as ADRs in decisions/.

ADR	Decision	Summary
001	Inherit the alknet TLS design	The alknet ADRs + crate spec are the baseline; deviations recorded as alktls ADRs
002	TlsError — ADR-088 shape from day one	Six typed variants, #[non_exhaustive], no string catch-all; config-construction scope boundary
003	The QUIC feature is noq	noq 1.2 (iroh's extracted fork) replaces quinn pre-consumer; iroh stays key-not-config
004	Complete the accessors	for_tcp_tls() adopted; server accessors borrow (&self), client accessors consume
005	Config types move into alktls	Identity + credentials + fingerprint move in; auth layer stays out
006	Module layout and test surface	Eight modules; in-module seed tests + integration invariant pins

Open Questions

Open questions are tracked in open-questions.md. All Phase 0 questions (OQ-TLS-01..08) were resolved at Phase 1 entry (2026-09-10) — six via ADR-001..006, two resolved as documented behavior (OQ-TLS-02, OQ-TLS-06); the tracker records the resolutions with pointers.

Components

• server.md — TlsServerConfig, resolvers, the ACME path, and the server-side invariants
• client.md — TlsClientConfig, verifier selection, client-auth presentation, the root-store fallback

Relationship to the alknet docs

The full design rationale lives in alknet's architecture docs (/workspace/@alkdev/alknet/docs/architecture/): ADR-082 (why a standalone TLS crate — the cert-reuse problem), ADR-083 (why the endpoint takes no TLS config), ADR-084 (why aws-lc-rs), ADR-027 (the identity model), ADR-034 (verifier selection), ADR-086 §3 (split ALPN lists), ADR-087 (TlsClientConfig), ADR-088 (TlsError, root-store fallback), ADR-089 (the dial seam), ADR-091 (ConnectionCredentials), and crates/tls/README.md (the full crate spec). alktls' ADR series records its own posture and points at the alknet reasoning rather than duplicating it.