response signing with auth key (#811)

* docs: spec for unifying response signing with auth key

Design для замены отдельной SignatureConfig на подпись ответов
RSA-ключом, взятым из auth.server.provider-private-key.

Made-with: Cursor

* docs: implementation plan for auth-based response signing

План реализации по спеке 2026-04-20-response-signing-with-auth-key-design.md.
Разбит на 9 задач: новые RsaSigner/DisabledSigner по TDD, переработка фабрики
под AuthorizationConfig, удаление SignatureConfig/signed-response, снятие
cache-гейта в EthereumLocalReader, обновление документации.

Made-with: Cursor

* feat(signature): add RsaSigner using SHA256withRSA

Made-with: Cursor

* feat(signature): add DisabledSigner that throws on sign()

Made-with: Cursor

* refactor(signature): ResponseSigner.sign returns non-null Signature

Made-with: Cursor

* refactor(signature): build signer from AuthorizationConfig

Made-with: Cursor

* refactor(config): remove signed-response YAML section and SignatureConfig

Made-with: Cursor

* refactor(signature): remove EcdsaSigner and NoSigner

Remove the obsolete ECDSA signer and the transitional NoSigner stub.
Replace NoSigner usages in tests with DisabledSigner, and pass
DisabledSigner to BroadcastReader in tests (signer is now non-null).

Made-with: Cursor

* refactor(local-reader): serve cached results for requests with nonce

Made-with: Cursor

* docs: replace signed-response with auth section incl. response signing

Made-with: Cursor

* docs: correct auth section YAML and expand Response Signing note

- docs/reference-configuration.adoc: fix the YAML shape of the auth
  section (server.keys.{provider-private-key,external-public-key} and
  publicKeyOwner) to match AuthorizationConfigReader, and expand the
  Response Signing subsection with the actual signed-message format.
- .gitignore: ignore /demo/response-signing/ (local sandbox with keys
  and generated gRPC stubs — regenerate with generate-keys.sh + protoc)
  and /docs/superpowers/ (specs/plans kept local-only for now). Any
  previously tracked files under these paths are untracked here.

Made-with: Cursor

* feat(upstream): auto-inject secure-signed label when signing is enabled

Expose ResponseSigner.enabled and thread the bean through UpstreamCreator
so Generic/Ethereum/Bitcoin creators can enrich each upstream's labels
with secure-signed=true whenever auth-backed response signing is active.
A user-provided value for the label is preserved.

Made-with: Cursor

docs/reference-configuration.adoc

@@ -47,10 +47,8 @@ cache:
     db: 0
     password: I1y0dGKy01by
 
-signed-response:
-  enabled: true
-  algorithm: SECP256K1
-  private-key: /path/key.pem
+auth:
+  enabled: false
 
 proxy:
   host: 0.0.0.0
@@ -207,10 +205,10 @@ See <<tokens>> section
 | Caching configuration.
 See <<cache>> section.
 
-| `signed-response`
+| `auth`
 |
-| Signed responses
-See <<signed-response>> section.
+| Authorization and response signing.
+See <<auth>> section.
 
 | `cluster`
 |
@@ -559,37 +557,66 @@ cache:
 
 |===
 
-[#signed-response]
-== Signed Response
+[#auth]
+== Authorization
+
+dshackle supports optional client authentication via signed JWT tokens (RS256). When
+`auth.enabled` is `true`, dshackle validates tokens issued by a trusted provider and
+rejects unauthenticated requests.
 
 [source,yaml]
 ----
-signed-response:
+auth:
   enabled: true
-  algorithm: SECP256K1
-  private-key: /path/key.pem
+  publicKeyOwner: "token-issuer-name"
+  server:
+    keys:
+      provider-private-key: "/etc/dshackle/auth/jwt-rsa.pem"
+      external-public-key: "/etc/dshackle/auth/jwt-rsa.pub"
 ----
 
-.Redis Config
-[cols="2a,2,5"]
 |===
-| Option | Default Value | Description
+| Name | Default | Description
 
 | `enabled`
 | `false`
-| Enable/disable Signed Responses
+| Enables authorization and response signing.
 
-| `algorithm`
-| `SECP256K1`
-| `SECP256K1` or `NIST-P256`
-
-| `private-key`
+| `publicKeyOwner`
 |
-| Path to a private key in PEM format
+| Expected value of the `iss` claim on inbound JWT tokens.
 
+| `server.keys.provider-private-key`
+|
+| Path to a PKCS#8 PEM RSA private key. Used both to sign session JWTs issued by
+  dshackle and to sign `NativeCall` response payloads (see <<response-signing>>).
+
+| `server.keys.external-public-key`
+|
+| Path to a PEM-encoded RSA public key (X.509 SubjectPublicKeyInfo) used to verify
+  the JWTs clients present to `emerald.Auth/Authenticate`.
 |===
 
-See more details at xref:07-methods.adoc#signatures[Signed Response]  in gRPC Methods.
+[#response-signing]
+==== Response Signing
+
+When `auth.enabled` is `true` and `auth.server.keys.provider-private-key` points to a
+valid PKCS#8 RSA private key, dshackle automatically signs gRPC responses with
+`SHA256withRSA` for any `NativeCall` request that provides a non-zero `nonce`. The same
+key used for issuing JWT tokens (RS256) is reused for response signatures — no separate
+configuration is required.
+
+The signed blob is `DSHACKLESIG/<nonce>/<upstream_id>/<hex-sha256(payload)>`. The
+returned `NativeCallReplySignature` carries the original `nonce`, the signature bytes
+and a `key_id` (first 8 bytes of the SHA-256 of the public key). Clients verify with
+the public half of `provider-private-key`.
+
+If a client sends a nonce but the signing key is not configured (auth disabled or the
+path is empty), dshackle returns an error with code `-32603` and message
+"Response signing requested via nonce but signing key is not configured".
+
+A runnable end-to-end example (dshackle config, demo RSA keys and a Go client) lives
+in `demo/response-signing/` in the repository.
 
 [#cluster]
 == Cluster