esp_http_client memory leak in esp_http_client_set_username/password (IDFGH-2306)

[AxelLin]

I'm checking the code in ESP-IDF-4.0-beta2:

In esp_http_client_set_username, it has below code:

if (username == NULL && client->connection_info.username != NULL) {
    free(client->connection_info.username);
    client->connection_info.username = NULL;
} else if (username != NULL) {
    client->connection_info.username = strdup(username);

Above code can cause memory leak when username != NULL && client->connection_info.username != NULL.
The same issue with esp_http_client_set_password.

e.g.
In esp_http_client/test/test_http_client.c
below test case will have memory leak.

TEST_CASE("Username and password will not reset if new absolute URL doesnot specify auth credentials.", "[ESP HTTP CLIENT]")
{
esp_http_client_config_t config_with_auth = {
.host = HOST,
.path = "/",
.username = USERNAME,
.password = PASSWORD
};
char *value = NULL;
esp_http_client_handle_t client = esp_http_client_init(&config_with_auth);
TEST_ASSERT_NOT_NULL(client);
esp_err_t r = esp_http_client_get_username(client, &value);
TEST_ASSERT_EQUAL(ESP_OK, r);
TEST_ASSERT_NOT_NULL(value);
TEST_ASSERT_EQUAL_STRING(USERNAME, value);
esp_http_client_set_url(client, "http://" HOST "/get");
esp_http_client_set_username(client, value);
esp_http_client_set_password(client, value);

BTW, since there are APIs to set_url/set_usernam/set_password,
why not also support set_authtype as well?

I post my proposed fix in attached file (including add set_authtype function):
esp_http_client_fix_memoryleak_and_allow_set_authtype_diff.txt

[mahavirj]

@AxelLin Is it possible for you to create pull request (based on fix you provided above)?