[EventEngine] Make oauth2 test utils work with EventEngine clients (#35866)

The Oauth2 credentials currently rely on pollsets and polling entities, partially because grpc_core::HttpRequest relies on them as well. This is a temporary solution to get both iomgr and EventEngine clients to pass the oauth2 interop tests.

Tested with the client experiment on and off.

Closes #35866

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35866 from drfloob:oauth2_utils_work_with_ee_hack 91eea0c196
PiperOrigin-RevId: 605433817

test/core/security/oauth2_utils.cc

@@ -29,6 +29,7 @@
 #include <grpc/support/sync.h>
 
 #include "src/core/lib/gprpp/crash.h"
+#include "src/core/lib/gprpp/notification.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/promise/exec_ctx_wakeup_scheduler.h"
 #include "src/core/lib/promise/map.h"
@@ -40,14 +41,14 @@ char* grpc_test_fetch_oauth2_token_with_credentials(
     grpc_call_credentials* creds) {
   grpc_core::ExecCtx exec_ctx;
   grpc_call_credentials::GetRequestMetadataArgs get_request_metadata_args;
-
+  // TODO(hork): rm once GetRequestMetadata does not depend on pollsets.
   grpc_pollset* pollset =
       static_cast<grpc_pollset*>(gpr_zalloc(grpc_pollset_size()));
   gpr_mu* mu = nullptr;
   grpc_pollset_init(pollset, &mu);
   auto pops = grpc_polling_entity_create_from_pollset(pollset);
   bool is_done = false;
-
+  grpc_core::Notification done;
   grpc_core::MemoryAllocator memory_allocator =
       grpc_core::MemoryAllocator(grpc_core::ResourceQuota::Default()
                                      ->memory_quota()
@@ -69,7 +70,7 @@ char* grpc_test_fetch_oauth2_token_with_credentials(
             });
       },
       grpc_core::ExecCtxWakeupScheduler(),
-      [&is_done, &token, &initial_metadata](absl::Status result) {
+      [&is_done, &done, &token, &initial_metadata](absl::Status result) {
         is_done = true;
         if (!result.ok()) {
           gpr_log(GPR_ERROR, "Fetching token failed: %s",
@@ -83,29 +84,31 @@ char* grpc_test_fetch_oauth2_token_with_credentials(
                       .value_or(""))
                   .c_str());
         }
+        done.Notify();
       },
       arena.get(), &pops);
-
   grpc_core::ExecCtx::Get()->Flush();
 
-  gpr_mu_lock(mu);
-  while (!is_done) {
-    grpc_pollset_worker* worker = nullptr;
-    if (!GRPC_LOG_IF_ERROR(
-            "pollset_work",
-            grpc_pollset_work(grpc_polling_entity_pollset(&pops), &worker,
-                              grpc_core::Timestamp::InfFuture()))) {
-      is_done = true;
+  if (grpc_core::IsEventEngineClientEnabled()) {
+    done.WaitForNotification();
+  } else {
+    gpr_mu_lock(mu);
+    while (!is_done) {
+      grpc_pollset_worker* worker = nullptr;
+      if (!GRPC_LOG_IF_ERROR(
+              "pollset_work",
+              grpc_pollset_work(grpc_polling_entity_pollset(&pops), &worker,
+                                grpc_core::Timestamp::InfFuture()))) {
+        is_done = true;
+      }
     }
+    gpr_mu_unlock(mu);
   }
-  gpr_mu_unlock(mu);
-
   grpc_pollset_shutdown(
       grpc_polling_entity_pollset(&pops),
       GRPC_CLOSURE_CREATE([](void*, grpc_error_handle) {}, nullptr, nullptr));
   grpc_core::ExecCtx::Get()->Flush();
   grpc_pollset_destroy(grpc_polling_entity_pollset(&pops));
   gpr_free(pollset);
-
   return token;
 }