fix: ApiKeyOption without UserProjectOption (#14748)

Author: dbolduc

google/cloud/internal/rest_set_metadata.cc

@@ -38,7 +38,7 @@ void SetMetadata(RestContext& context, Options const& options,
   if (options.has<QuotaUserOption>()) {
     context.AddHeader("x-goog-quota-user", options.get<QuotaUserOption>());
   }
-  if (options.has<UserProjectOption>()) {
+  if (options.has<ApiKeyOption>()) {
     context.AddHeader("x-goog-api-key", options.get<ApiKeyOption>());
   }
   if (options.has<FieldMaskOption>()) {

google/cloud/internal/rest_set_metadata_test.cc

@@ -25,6 +25,7 @@ namespace rest_internal {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
 namespace {
 
+using ::testing::Contains;
 using ::testing::ElementsAre;
 using ::testing::Pair;
 using ::testing::UnorderedElementsAre;
@@ -71,6 +72,14 @@ TEST(RestContextTest, SetMetadataFull) {
                   Pair("custom-header-2", ElementsAre("v2"))));
 }
 
+TEST(RestContextTest, Regression14745) {
+  RestContext lhs;
+  SetMetadata(lhs, Options{}.set<ApiKeyOption>("api-key"), {},
+              "api-client-header");
+  EXPECT_THAT(lhs.headers(),
+              Contains(Pair("x-goog-api-key", ElementsAre("api-key"))));
+}
+
 }  // namespace
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace rest_internal