setopt: clear proxy auth properly on NULL

Verify NULLed proxy credentials with test1648

Closes #21696

tests/libtest/Makefile.inc

@@ -99,7 +99,7 @@ TESTS_C = \
   lib1576.c lib1582.c lib1587.c lib1588.c lib1589.c \
   lib1591.c lib1592.c lib1593.c lib1594.c                     lib1597.c \
   lib1598.c lib1599.c \
-  lib1647.c \
+  lib1647.c lib1648.c \
   lib1662.c \
   lib1900.c lib1901.c lib1902.c lib1903.c lib1905.c lib1906.c lib1907.c \
   lib1908.c           lib1910.c lib1911.c lib1912.c lib1913.c \

tests/libtest/lib1648.c

@@ -0,0 +1,135 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ * SPDX-License-Identifier: curl
+ *
+ ***************************************************************************/
+/*
+ * URL = host
+ * arg2 = port
+ */
+
+#include "first.h"
+
+/* this is meant to pick up the proxy from the environment variable */
+static CURLcode init1648(CURL *curl, const char *url, const char *proxy)
+{
+  CURLcode result = CURLE_OK;
+
+  res_easy_setopt(curl, CURLOPT_URL, url);
+  if(result)
+    goto init_failed;
+
+  res_easy_setopt(curl, CURLOPT_PROXY, proxy);
+  if(result)
+    goto init_failed;
+
+  res_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
+  if(result)
+    goto init_failed;
+
+  return CURLE_OK; /* success */
+
+init_failed:
+  return result; /* failure */
+}
+
+static CURLcode run1648(CURL *curl, const char *url, const char *userpwd)
+{
+  CURLcode result = CURLE_OK;
+
+  result = init1648(curl, url, userpwd);
+  if(result)
+    return result;
+
+  return curl_easy_perform(curl);
+}
+
+#define GET_THIS "http://example.com/"
+
+/*
+ * First get the URL over 'firstproxy' with auth.
+ * Then clear the auth and get the URL again over 'secondproxy'.
+ */
+static CURLcode test_lib1648(const char *hostip)
+{
+  CURLcode result = CURLE_OK;
+  CURL *curl = NULL;
+  struct curl_slist *host = NULL;
+  struct curl_slist *host2 = NULL;
+  char proxy1_resolve[128];
+  char proxy2_resolve[128];
+  char proxy1_connect[128];
+  char proxy2_connect[128];
+
+  curl_msnprintf(proxy1_resolve, sizeof(proxy1_resolve),
+                 "firstproxy:%s:%s", libtest_arg2, hostip);
+  curl_msnprintf(proxy2_resolve, sizeof(proxy2_resolve),
+                 "secondproxy:%s:%s", libtest_arg2, hostip);
+
+  /* we connect to the fake host name but the right port number */
+  curl_msnprintf(proxy1_connect, sizeof(proxy1_connect),
+                 "firstproxy:%s", libtest_arg2);
+  curl_msnprintf(proxy2_connect, sizeof(proxy2_connect),
+                 "secondproxy:%s", libtest_arg2);
+
+  res_global_init(CURL_GLOBAL_ALL);
+  if(result)
+    return result;
+
+  curl = curl_easy_init();
+  if(!curl) {
+    curl_mfprintf(stderr, "curl_easy_init() failed\n");
+    curl_global_cleanup();
+    return TEST_ERR_MAJOR_BAD;
+  }
+
+  host = curl_slist_append(NULL, proxy1_resolve);
+  if(!host)
+    goto test_cleanup;
+  host2 = curl_slist_append(host, proxy2_resolve);
+  if(!host2)
+    goto test_cleanup;
+  host = host2;
+
+  start_test_timing();
+
+  easy_setopt(curl, CURLOPT_RESOLVE, host);
+  easy_setopt(curl, CURLOPT_PROXYUSERPWD, "victim:secret");
+
+  curl_mprintf("--- First get over %s\n", proxy1_connect);
+  result = run1648(curl, GET_THIS, proxy1_connect);
+  if(result)
+    goto test_cleanup;
+
+  easy_setopt(curl, CURLOPT_PROXYUSERPWD, NULL);
+
+  curl_mprintf("--- Then over '%s'\n", proxy2_connect);
+  result = run1648(curl, GET_THIS, proxy2_connect);
+
+test_cleanup:
+
+  /* proper cleanup sequence - type PB */
+
+  curl_easy_cleanup(curl);
+  curl_global_cleanup();
+  curl_slist_free_all(host);
+  return result;
+}