Signed requests: strictly increasing timestamps per key

Ed25519 signatures are deterministic, so two identical requests from one key in the same
millisecond (e.g. two devices subscribing to the same path, or parallel identical reads)
had the same signature, and the server rejected the second as a replay.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Qxbkp4tA7G5SCWjzWuxmE

test/utils/request-auth.test.ts

@@ -24,7 +24,7 @@ describe('RequestAuth', () => {
     await expect(auth.verify(await signed(signer), '/kv/readMany', '{"keys":["b"]}')).rejects.toThrow(/Invalid signature/)
     await expect(auth.verify(await signed(signer), '/kv/writeMany', '{"keys":["a"]}')).rejects.toThrow(/Invalid signature/)
     const headers = await signed(signer)
-    headers.set(AUTH_HEADERS.timestamp, String(NOW + 1))
+    headers.set(AUTH_HEADERS.timestamp, String(Number(headers.get(AUTH_HEADERS.timestamp)) + 1))
     await expect(auth.verify(headers, '/kv/readMany', '{"keys":["a"]}')).rejects.toThrow(/Invalid signature/)
     const other = await Ed25519Signer.generate()
     const swapped = await signed(signer)
@@ -32,11 +32,20 @@ describe('RequestAuth', () => {
     await expect(auth.verify(swapped, '/kv/readMany', '{"keys":["a"]}')).rejects.toThrow(/Invalid signature/)
   })
 
+  it('accepts identical requests made in the same millisecond (timestamps per key increase)', async () => {
+    const signer = await Ed25519Signer.generate()
+    const sameKey = await Ed25519Signer.fromPrivateKey(await signer.exportPrivateKey())
+    const auth = new RequestAuth([new Ed25519Verifier()], { now: () => NOW })
+    const requests = await Promise.all([signed(signer), signed(signer), signed(sameKey)])
+    expect(new Set(requests.map((h) => h.get(AUTH_HEADERS.signature))).size).toBe(3)
+    for (const headers of requests) expect(await auth.verify(headers, '/kv/readMany', '{"keys":["a"]}')).toBe(signer.publicKey)
+  })
+
   it('rejects old or future timestamps, replays, missing headers and unknown algorithms', async () => {
     const signer = await Ed25519Signer.generate()
     const auth = new RequestAuth([new Ed25519Verifier()], { now: () => NOW, maxSkewMs: 1000 })
-    await expect(auth.verify(await signed(signer, '/p', 'b', NOW - 5000), '/p', 'b')).rejects.toThrow(/window/)
-    await expect(auth.verify(await signed(signer, '/p', 'b', NOW + 5000), '/p', 'b')).rejects.toThrow(/window/)
+    await expect(auth.verify(await signed(await Ed25519Signer.generate(), '/p', 'b', NOW - 5000), '/p', 'b')).rejects.toThrow(/window/)
+    await expect(auth.verify(await signed(await Ed25519Signer.generate(), '/p', 'b', NOW + 5000), '/p', 'b')).rejects.toThrow(/window/)
     const once = await signed(signer, '/p', 'b')
     await auth.verify(once, '/p', 'b')
     await expect(auth.verify(once, '/p', 'b')).rejects.toThrow(/Replayed/)