test: avoid use after free in oauth_integration_test (envoyproxy#14103)

The client request stream can be deleted under the call stack of Envoy::IntegrationCodecClient::startRequest if the proxy replies quickly enough. Attempts to send an end stream on that request result in use-after-free on the client stream in cases where the client processed the full reply inside startRequest.

Fixes envoyproxy#12960

Signed-off-by: Antonio Vicente <avd@google.com>
Signed-off-by: Christoph Pakulski <christoph@tetrate.io>

test/extensions/filters/http/oauth2/oauth_integration_test.cc

@@ -91,8 +91,6 @@ TEST_F(OauthIntegrationTest, UnauthenticatedFlow) {
                                          {":authority", "authority"}};
   auto encoder_decoder = codec_client_->startRequest(headers);
 
-  Buffer::OwnedImpl buffer;
-  encoder_decoder.first.encodeData(buffer, true);
   request_encoder_ = &encoder_decoder.first;
   auto response = std::move(encoder_decoder.second);
 
@@ -144,4 +142,4 @@ TEST_F(OauthIntegrationTest, AuthenticationFlow) {
 } // namespace Oauth
 } // namespace HttpFilters
 } // namespace Extensions
-} // namespace Envoy
+} // namespace Envoy