diff --git a/google/cloud/internal/oauth2_impersonate_service_account_credentials.cc b/google/cloud/internal/oauth2_impersonate_service_account_credentials.cc
index 16dfbb286a0d6..0af7f2852324e 100644
--- a/google/cloud/internal/oauth2_impersonate_service_account_credentials.cc
+++ b/google/cloud/internal/oauth2_impersonate_service_account_credentials.cc
@@ -67,24 +67,7 @@ ParseImpersonatedServiceAccountCredentials(std::string const& content,
   }
   // We strip the service account from the path URL.
   auto url = it->get<std::string>();
-  auto colon = url.rfind(':');
-  if (colon == std::string::npos) {
-    return internal::InvalidArgumentError(
-        "Malformed `service_account_impersonation_url` field contents on data "
-        "from " +
-            source,
-        GCP_ERROR_INFO());
-  }
-  if (url.substr(colon) != ":generateAccessToken") {
-    // While `generateIdToken` is a valid RPC, we do not currently support ID
-    // token flow. So we might as well error when parsing the credentials.
-    return internal::InvalidArgumentError(
-        "Only access token authentication is supported for impersonated "
-        "service accounts from " +
-            source,
-        GCP_ERROR_INFO());
-  }
-  auto slash = url.rfind('/', colon);
+  auto slash = url.rfind('/');
   if (slash == std::string::npos) {
     return internal::InvalidArgumentError(
         "Malformed `service_account_impersonation_url` field contents on data "
@@ -92,7 +75,13 @@ ParseImpersonatedServiceAccountCredentials(std::string const& content,
             source,
         GCP_ERROR_INFO());
   }
-  info.service_account = std::string{url.substr(slash + 1, colon - slash - 1)};
+
+  // In the url, after the last slash, it is in the format of
+  // `service_account[:action]`
+  auto service_account_action = url.substr(slash + 1);
+  auto colon = service_account_action.rfind(':');
+  auto end = colon == std::string::npos ? service_account_action.size() : colon;
+  info.service_account = service_account_action.substr(0, end);
 
   it = credentials.find("delegates");
   if (it != credentials.end()) {
diff --git a/google/cloud/internal/oauth2_impersonate_service_account_credentials_test.cc b/google/cloud/internal/oauth2_impersonate_service_account_credentials_test.cc
index 96563806cf687..f626d85cf7309 100644
--- a/google/cloud/internal/oauth2_impersonate_service_account_credentials_test.cc
+++ b/google/cloud/internal/oauth2_impersonate_service_account_credentials_test.cc
@@ -50,6 +50,19 @@ auto constexpr kFullValidConfig = R"""({
   "type": "impersonated_service_account"
 })""";
 
+auto constexpr kFullValidConfigNoAction = R"""({
+  "service_account_impersonation_url": "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/sa3@developer.gserviceaccount.com",
+  "delegates": [
+    "sa1@developer.gserviceaccount.com",
+    "sa2@developer.gserviceaccount.com"
+  ],
+  "quota_project_id": "my-project",
+  "source_credentials": {
+    "type": "authorized_user"
+  },
+  "type": "impersonated_service_account"
+})""";
+
 TEST(ParseImpersonatedServiceAccountCredentials, Success) {
   auto actual =
       ParseImpersonatedServiceAccountCredentials(kFullValidConfig, "test-data");
@@ -146,6 +159,19 @@ TEST(ImpersonateServiceAccountCredentialsTest, Basic) {
   ASSERT_THAT(token, StatusIs(StatusCode::kPermissionDenied));
 }
 
+TEST(ParseImpersonatedServiceAccountCredentialsWithoutAction, Success) {
+  auto actual = ParseImpersonatedServiceAccountCredentials(
+      kFullValidConfigNoAction, "test-data");
+  ASSERT_STATUS_OK(actual);
+  EXPECT_EQ(actual->service_account, "sa3@developer.gserviceaccount.com");
+  EXPECT_THAT(actual->delegates,
+              ElementsAre("sa1@developer.gserviceaccount.com",
+                          "sa2@developer.gserviceaccount.com"));
+  EXPECT_THAT(actual->quota_project_id, Optional<std::string>("my-project"));
+  EXPECT_THAT(actual->source_credentials,
+              AllOf(HasSubstr("type"), HasSubstr("authorized_user")));
+}
+
 }  // namespace
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace oauth2_internal