Keep a route's headers on the HTTPS upgrade its probe follows

A route probe follows an upgrade to HTTPS on the server's host, as the API client does, but the health client dropped the route's own headers -- an access token for the proxy in front, say -- from any request away from the route's origin, that upgrade included. The server answered the probe's second request with its sign-in, and a working route was taken not to answer. The headers now go where the API client sends them: the route's origin, and that upgrade on its host. The logout fence still keeps the cookie off.

packages/conduit_core/lib/services/connectivity_service.dart

@@ -696,8 +696,15 @@ Dio createConnectivityHealthClient(
     dio.interceptors.add(
       InterceptorsWrapper(
         onRequest: (options, handler) {
-          if (ConnectivityService._originKey(options.uri) !=
-              ConnectivityService._originKey(serverUri)) {
+          // Kept where the API client keeps them: the server's own origin,
+          // or an upgrade to HTTPS on its host that a probe follows.
+          final target = options.uri;
+          final sameServer =
+              ConnectivityService._originKey(target) ==
+                  ConnectivityService._originKey(serverUri) ||
+              (serverUri != null &&
+                  isCredentialSafeRedirectTarget(serverUri, target));
+          if (!sameServer) {
             options.headers.removeWhere(
               (name, _) => customHeaderNames.contains(name.toLowerCase()),
             );

test/core/services/connectivity_service_lifecycle_test.dart

@@ -223,6 +223,28 @@ void main() {
     }, _RealHttpOverrides());
   });
 
+  // A probe follows an upgrade to HTTPS on the server's host, as the API
+  // client does; the route's own headers go with it, and nowhere else.
+  test('health client keeps the route headers on an upgrade to HTTPS', () async {
+    final dio = createConnectivityHealthClient(
+      const ServerConfig(
+        id: 'route',
+        name: 'Route',
+        url: 'http://chat.example',
+        customHeaders: {'CF-Access-Client-Id': 'route-id'},
+      ),
+    );
+    addTearDown(dio.close);
+    final sent = <String, Object?>{};
+    dio.httpClientAdapter = _HeaderRecorder(sent);
+
+    await dio.getUri<dynamic>(Uri.parse('https://chat.example/health'));
+    await dio.getUri<dynamic>(Uri.parse('https://other.example/health'));
+
+    check(sent['https://chat.example/health']).equals('route-id');
+    check(sent['https://other.example/health']).isNull();
+  });
+
   group('a route probe', () {
     /// Serves [handle] on a loopback port for the length of the test.
     Future<String> serve(
@@ -734,3 +756,32 @@ final class _FailingHealthAdapter implements _RequestCountingAdapter {
 }
 
 final class _RealHttpOverrides extends HttpOverrides {}
+
+/// Records the route header each request went out with, by URL.
+final class _HeaderRecorder implements HttpClientAdapter {
+  _HeaderRecorder(this.sent);
+
+  final Map<String, Object?> sent;
+
+  @override
+  Future<ResponseBody> fetch(
+    RequestOptions options,
+    Stream<Uint8List>? requestStream,
+    Future<void>? cancelFuture,
+  ) async {
+    sent[options.uri.toString()] = options.headers.entries
+        .where((entry) => entry.key.toLowerCase() == 'cf-access-client-id')
+        .map((entry) => entry.value)
+        .firstOrNull;
+    return ResponseBody.fromString(
+      '{"status":true}',
+      HttpStatus.ok,
+      headers: {
+        Headers.contentTypeHeader: [Headers.jsonContentType],
+      },
+    );
+  }
+
+  @override
+  void close({bool force = false}) {}
+}