Add azure-deprecating to default allowed headers for logging

Add `azure-deprecating` to the default set of response headers that are
logged without redaction in the Azure Core HTTP pipeline sanitizer.

The `azure-deprecating` header is used per the Azure API Guidelines
deprecating behavior notification guidance to notify clients about
upcoming API deprecations. Without this change, the header value would
be logged as REDACTED, hiding important deprecation warnings.

- Add azure-deprecating to defaultAllowedHeaderNames in sanitizer.ts
- Update sdk/core/logger/README.md to keep the documented list in sync
- Add test verifying azure-deprecating is not redacted
- Update ts-http-runtime CHANGELOG

Co-authored-by: heaths <1532486+heaths@users.noreply.github.com>

Author: Copilot

sdk/core/logger/README.md

@@ -51,6 +51,7 @@ Request and response bodies are never logged. Headers are redacted by default, u
 - "ms-cv",
 - "return-client-request-id",
 - "traceparent",
+- "azure-deprecating",
 - "Access-Control-Allow-Credentials",
 - "Access-Control-Allow-Headers",
 - "Access-Control-Allow-Methods",

sdk/core/ts-http-runtime/CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Features Added
 
+- `azure-deprecating` response header is now included in the default set of headers logged without redaction. See [Azure API Guidelines: Deprecating Behavior Notification](https://github.com/microsoft/api-guidelines/blob/vNext/azure/Guidelines.md#deprecating-behavior-notification) for more information.
+
 ### Breaking Changes
 
 ### Bugs Fixed

sdk/core/ts-http-runtime/src/util/sanitizer.ts

@@ -35,6 +35,7 @@ const defaultAllowedHeaderNames = [
   "ms-cv",
   "return-client-request-id",
   "traceparent",
+  "azure-deprecating",
 
   "Access-Control-Allow-Credentials",
   "Access-Control-Allow-Headers",

sdk/core/ts-http-runtime/test/internal/logPolicy.spec.ts

@@ -40,4 +40,25 @@ describe("logPolicy", function () {
     assert.notInclude(headersLog!, "secret-value");
     assert.include(headersLog!, "REDACTED");
   });
+
+  it("Does not redact the azure-deprecating response header", async function () {
+    const { logger, logs } = createTestLogger();
+    const policy = logPolicy({ logger });
+
+    const request = createPipelineRequest({ url: "https://example.com" });
+    const responseHeaders = createHttpHeaders({
+      "azure-deprecating": "This API version will be retired on 2025-01-01",
+    });
+
+    await policy.sendRequest(request, async (req) => ({
+      request: req,
+      status: 200,
+      headers: responseHeaders,
+    }));
+
+    const headersLog = logs.find((log) => log.startsWith("Headers:"));
+    assert.isDefined(headersLog);
+    assert.include(headersLog!, "This API version will be retired on 2025-01-01");
+    assert.notInclude(headersLog!, "REDACTED");
+  });
 });