test: add NIP-98 edge cases — replay, future clock drift, URL path mismatch

Documents finding: no replay protection in NIP-98 verification.
Token replay within 120s window succeeds (mitigated by JWT issuance being idempotent).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/middleware/nip98.test.ts

@@ -120,4 +120,44 @@ describe('verifyNip98Token', () => {
     expect(result.valid).toBe(false)
     expect(result.error).toContain('Wrong event kind')
   })
+
+  it('token replay: same valid token accepted twice within 120s (no replay protection)', () => {
+    // FINDING: NIP-98 spec doesn't mandate replay protection.
+    // The server verifies signature and timestamp but does not track seen event IDs.
+    // A valid token can be replayed within its 120s window.
+    // Mitigation: JWT is issued on first use, so replay only re-issues JWT for same pubkey.
+    const sk = generateSecretKey()
+    const event = createNip98Event(sk, 'https://example.com/api/auth', 'POST')
+    const header = toAuthHeader(event)
+
+    const result1 = verifyNip98Token(header, '/api/auth', 'POST')
+    const result2 = verifyNip98Token(header, '/api/auth', 'POST')
+    expect(result1.valid).toBe(true)
+    expect(result2.valid).toBe(true) // No replay protection — documenting behavior
+  })
+
+  it('rejects clock drift >120s in the future', () => {
+    const sk = generateSecretKey()
+    const event = finalizeEvent({
+      kind: 27235,
+      created_at: Math.floor(Date.now() / 1000) + 200, // 200s in the future
+      tags: [['u', 'https://example.com/api/auth'], ['method', 'POST']],
+      content: '',
+    }, sk)
+    const header = toAuthHeader(event)
+
+    const result = verifyNip98Token(header, '/api/auth', 'POST')
+    expect(result.valid).toBe(false)
+    expect(result.error).toContain('expired')
+  })
+
+  it('rejects URL path mismatch', () => {
+    const sk = generateSecretKey()
+    const event = createNip98Event(sk, 'https://example.com/api/auth/login', 'POST')
+    const header = toAuthHeader(event)
+
+    const result = verifyNip98Token(header, '/api/auth/session', 'POST')
+    expect(result.valid).toBe(false)
+    expect(result.error).toContain('URL path mismatch')
+  })
 })