fix(secrets): Do not treat x-session-affinity as a credential

README.md

@@ -125,8 +125,9 @@ A run takes `RunConfig` (`src/service.ts`): `tenant`, `mode`, `rules`,
   goes to a model in a prompt. The service keeps them only in memory, for
   the run. A run can have 32 of them. It also learns the value of each request header whose name can mean a credential,
   such as one with `auth`, `token`, `key`, `secret`, `cookie`, or `session`.
-  The match is broad on purpose. Recordings show `<<redacted>>` in place of
-  each known value.
+  The match is broad on purpose. It does not learn `x-session-affinity`,
+  because that header has a conversation id and not a credential.
+  Recordings show `<<redacted>>` in place of each known value.
 
 Requests that match no rule go live without a change, and their responses
 stream. Each response has an `x-roach` header: `replayed`, `live`,

src/secrets.ts

@@ -13,6 +13,14 @@ import type { IncomingHttpHeaders } from "node:http";
  */
 const CREDENTIAL_HEADER =
   /auth|token|secret|key|cookie|session|password|credential|signature/i;
+/**
+ * Headers that match `CREDENTIAL_HEADER` but carry no credential. A response
+ * can show their values, and the client must get them back without a change.
+ * AI Gateway clients put a conversation id in `x-session-affinity`, and a
+ * model can repeat that id in its response. Node gives header names in
+ * lower case.
+ */
+const NOT_CREDENTIAL_HEADERS = new Set(["x-session-affinity"]);
 /** Shorter parts, such as `Bearer`, are not credentials. */
 const MIN_LENGTH = 12;
 const REDACTED = "<<redacted>>";
@@ -41,6 +49,7 @@ export function createSecrets(initial: string[] = []) {
     learn(headers: IncomingHttpHeaders): void {
       for (const [name, value] of Object.entries(headers)) {
         if (!CREDENTIAL_HEADER.test(name) || value === undefined) continue;
+        if (NOT_CREDENTIAL_HEADERS.has(name)) continue;
         for (const item of Array.isArray(value) ? value : [value]) add(item);
       }
     },

tests/service.test.ts

@@ -91,6 +91,7 @@ beforeEach(async () => {
         n: liveRequests,
         key: incoming.headers["x-api-key"] ?? null,
         echo: incoming.headers["x-echo"] ?? null,
+        affinity: incoming.headers["x-session-affinity"] ?? null,
         serviceSecret: "service-secret-value-123",
       }),
     );
@@ -386,6 +387,7 @@ describe("roach service", () => {
       n: 1,
       key: "<<redacted>>",
       echo: "<<redacted>>",
+      affinity: null,
       serviceSecret: "<<redacted>>",
     });
     const [file] = await recordings("acme/alpha");
@@ -397,4 +399,30 @@ describe("roach service", () => {
     expect(text).not.toContain("service-secret-value-123");
     expect(text).not.toContain("run-secret-value-789");
   });
+
+  it("does not redact the session affinity header", async () => {
+    // AI Gateway clients send a conversation id in `x-session-affinity`.
+    // It is not a credential, and the client must get it back as it is.
+    const run = await startRun("write-token", "auto");
+    const response = await send(
+      run.url,
+      { prompt: "hi" },
+      {
+        "x-api-key": "sk-live-request-key-456",
+        "x-session-affinity": "conversation-id-0123456789",
+      },
+    );
+
+    expect(JSON.parse(response.body)).toMatchObject({
+      key: "<<redacted>>",
+      affinity: "conversation-id-0123456789",
+    });
+    const [file] = await recordings("acme/alpha");
+    const text = await readFile(
+      path.join(directory, "acme/alpha", "model", file!),
+      "utf8",
+    );
+    expect(text).toContain("conversation-id-0123456789");
+    expect(text).not.toContain("sk-live-request-key-456");
+  });
 });