impl(universe_domain): update implementation to reflect testing results (#13530)

Author: scotthart

google/cloud/internal/compute_engine_util.cc

@@ -25,7 +25,7 @@ std::string GceMetadataScheme() { return "http"; }
 
 std::string GceMetadataHostname() {
   return google::cloud::internal::GetEnv(GceMetadataHostnameEnvVar())
-      .value_or("metadata.google.internal.");
+      .value_or("metadata.google.internal");
 }
 
 }  // namespace internal

google/cloud/internal/compute_engine_util_test.cc

@@ -33,7 +33,7 @@ TEST(ComputeEngineUtilTest, CanOverrideGceMetadataHostname) {
   // If not overridden for testing, we should get the actual hostname.
   google::cloud::testing_util::ScopedEnvironment gce_metadata_hostname_unset(
       GceMetadataHostnameEnvVar(), {});
-  EXPECT_EQ(std::string("metadata.google.internal."), GceMetadataHostname());
+  EXPECT_EQ(std::string("metadata.google.internal"), GceMetadataHostname());
 }
 
 }  // namespace

google/cloud/internal/oauth2_compute_engine_credentials.cc

@@ -263,9 +263,11 @@ StatusOr<std::string> ComputeEngineCredentials::RetrieveUniverseDomain(
     }
     return AsStatus(std::move(**response));
   }
-  auto metadata = ParseMetadataServerResponse(**response);
-  if (!metadata) return std::move(metadata).status();
-  universe_domain_ = std::move(metadata->universe_domain);
+
+  auto payload =
+      rest_internal::ReadAll((std::move(**response)).ExtractPayload());
+  if (!payload.ok()) return payload.status();
+  universe_domain_ = *std::move(payload);
   return *universe_domain_;
 }
 

google/cloud/internal/oauth2_compute_engine_credentials_test.cc

@@ -430,9 +430,7 @@ auto expected_universe_domain_request = []() {
 };
 
 TEST(ComputeEngineCredentialsTest, UniverseDomainSuccess) {
-  auto const universe_domain_resp = std::string{R"""({
-      "universe_domain": "my-ud.net"
-  })"""};
+  auto const universe_domain_resp = std::string{R"""(my-ud.net)"""};
 
   auto client = std::make_unique<MockRestClient>();
   EXPECT_CALL(*client, Get(_, expected_universe_domain_request()))

google/cloud/internal/unified_rest_credentials_test.cc

@@ -245,7 +245,7 @@ TEST(UnifiedRestCredentialsTest, AdcIsComputeEngine) {
     auto client = std::make_unique<MockRestClient>();
     auto expected_request = AllOf(
         Property(&RestRequest::path,
-                 absl::StrCat("http://metadata.google.internal./",
+                 absl::StrCat("http://metadata.google.internal/",
                               "computeMetadata/v1/instance/service-accounts/",
                               "default/")),
         Property(&RestRequest::headers,
@@ -259,7 +259,7 @@ TEST(UnifiedRestCredentialsTest, AdcIsComputeEngine) {
     auto client = std::make_unique<MockRestClient>();
     auto expected_request = AllOf(
         Property(&RestRequest::path,
-                 absl::StrCat("http://metadata.google.internal./",
+                 absl::StrCat("http://metadata.google.internal/",
                               "computeMetadata/v1/instance/service-accounts/",
                               "default/", "token")),
         Property(&RestRequest::headers,