Release v1.0.0

Cirreum.SignedRequest 1.0.0 — the shared RFC 9421 / RFC 9530 core

The dependency-free primitives for HTTP Message Signatures (RFC 9421) and
Content-Digest (RFC 9530): the shared signature base, the wire parser, the digest
compute/verify, the pluggable algorithm seam, and the outbound signer. This is the
common language spoken by the Cirreum.Authentication.SignedRequest server scheme
and the Cirreum.Authentication.SignedRequest.Client SDK, so a request signed on one
side verifies byte-for-byte on the other.

Strictly additive — initial release. No dependencies beyond the BCL.

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Why this release exists

RFC 9421 only interoperates when the signer and the verifier reconstruct the exact
same signature base. When those two live in different packages — one signing
outbound webhooks / API calls, one verifying inbound requests — the canonicalization
rules (method casing, percent-encoding, @path / @query normalization, the
@signature-params line) have to agree to the byte. The way to guarantee that is to
give both sides one implementation rather than two that are "kept in sync."

Cirreum.SignedRequest is that one implementation. It is pure BCL — no Cirreum,
ASP.NET, or third-party dependencies — so both the server scheme and the standalone
client SDK reference it and can never drift.

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What's new

SignatureBaseBuilder

var signing = SignatureBaseBuilder.BuildForSigning(components, parameters);
// signer: HMAC over signing.SignatureBase; emit Signature / Signature-Input
var baseBytes = SignatureBaseBuilder.BuildBase(components, entry.CoveredComponents, entry.SignatureParamsValue);
// verifier: rebuild the byte-identical base from the received params, then verify

Builds the RFC 9421 signature base (the ordered, labelled "component": value lines
terminated by "@signature-params"). The verifier replays the received params
verbatim, so its reconstructed base is byte-identical to what was signed.

SignatureBaseComponents.FromRequest(method, path, query, fields)

The single value normalizer — method casing, @path / @query to their RFC 9421
§2.2.6/§2.2.7 + RFC 3986 §6.2.2 canonical form, empty-path default, case-insensitive
field keys. Both sides project their host request onto it, so canonicalization lives
in exactly one place. @path is bound in dot-segment-normalized form; authorization
keys on the normalized path.

SignatureWireParser / ParsedSignature

Defensive RFC 8941 parsing of the Signature / Signature-Input structured-field
headers. Every malformation returns false rather than throwing; duplicate dictionary
labels / parameters are rejected.

ContentDigest

RFC 9530 Content-Digest compute and constant-time verify (SHA-256), binding the
request body into the signature regardless of method.

ISignedRequestAlgorithm / ISignedRequestAlgorithmResolver

The pluggable signing / verification seam, with HmacSha256SignedRequestAlgorithm
(hmac-sha256) built in. Additional algorithms (e.g. Ed25519) register additively
without touching the signature base or wire format.

The outbound signer

// Sign a prepared request:
await request.SignRequestAsync(keyId, signingSecret);

// Or sign + send with a JSON body in one call:
var response = await client.SendSignedAsync(
    HttpMethod.Post, "/v1/events", keyId, signingSecret, new { eventType = "order.placed", id });

HttpRequestMessage.SignRequestAsync(...) / HttpClient.SendSignedAsync(...) (in
System.Net.Http, so they surface ambiently), with OutboundSigningOptions and
SigningCredentials. This is the single signer the server scheme (outbound webhooks)
and the client SDK (outbound API calls) both use — built on SignatureBaseBuilder, so
the signer cannot drift from the verifier.

SignedRequestHeaders

The RFC 9421 / RFC 9530 header names (Signature, Signature-Input, Content-Digest)
in one place, referenced by the signer and the server verifier so they never diverge.

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Compatibility

• Strictly additive. Initial release.
• No dependencies beyond the BCL — no Cirreum, ASP.NET, or third-party packages.
• Conformance is verified against RFC 4231 (HMAC-SHA-256) and RFC 9530
  (Content-Digest) published test vectors; the signature base is locked by a
  known-answer vector; the wire parser is fuzz-hardened against the RFC 9421 §7
  never-throw contract.

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Coordinated downstream work

This release unblocks the first releases of Cirreum.Authentication.SignedRequest.Client
(SDK — depends only on this package) and Cirreum.Authentication.SignedRequest (server
scheme — depends on this package plus the auth foundation).

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See also

• Cirreum.Authentication.SignedRequest — the server scheme (verify inbound, sign outbound webhooks)
• Cirreum.Authentication.SignedRequest.Client — the consumer SDK (sign outbound calls, validate inbound webhooks)