Add test for MXS-2355

The test attempts to log in using mysql_clear_password.

maxscale-system-test/CMakeLists.txt

@@ -210,6 +210,9 @@ add_test_executable(kill_query.cpp kill_query replication LABELS REPL_BACKEND)
 # MXS-2250: DESCRIBE on temporary table should work.
 add_test_executable(mxs2250_describe_temp_table.cpp mxs2250_describe_temp_table mxs2250_describe_temp_table LABELS REPL_BACKEND)
 
+# MXS-2355: Try to log in using a different authentication plugin
+add_test_executable(mxs2355_wrong_auth.cpp mxs2355_wrong_auth maxctrl LABELS REPL_BACKEND)
+
 ############################################
 # BEGIN: Tests that require GTID           #
 ############################################

maxscale-system-test/mxs2355_wrong_auth.cpp

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2019 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include "testconnections.h"
+
+// Try to connect with mysql client using the plugin "mysql_clear_password". MaxScale should switch back
+// to "mysql_native_password".
+
+int main(int argc, char** argv)
+{
+    TestConnections test(argc, argv);
+    const char* host = test.maxscales->IP[0];
+    int port = test.maxscales->ports[0][0];
+    const char* user = test.maxscales->user_name;
+    const char* pass = test.maxscales->password;
+    const char plugin[] = "mysql_clear_password";
+
+    test.tprintf("Trying to log in to [%s]:%i as %s with plugin '%s'.\n", host, port, user, plugin);
+    MYSQL* maxconn = mysql_init(NULL);
+    test.expect(maxconn, "mysql_init failed");
+    if (maxconn)
+    {
+        // Need to set plugin directory so that mysql_clear_password is found.
+        const char plugin_path[] = "../connector-c/install/lib/mariadb/plugin";
+        mysql_optionsv(maxconn, MYSQL_PLUGIN_DIR, plugin_path);
+        mysql_optionsv(maxconn, MYSQL_DEFAULT_AUTH, plugin);
+        mysql_real_connect(maxconn, host, user, pass, NULL, port, NULL, 0);
+        auto err = mysql_error(maxconn);
+        if (*err)
+        {
+            test.expect(false, "Could not log in: '%s'", err);
+        }
+        else
+        {
+            test.try_query(maxconn, "SELECT rand();");
+            if (test.ok())
+            {
+                test.tprintf("Logged in and queried successfully.\n");
+                test.log_includes(0, "is using an unsupported authenticator plugin 'mysql_clear_password'.");
+            }
+            else
+            {
+                test.tprintf("Query rejected: '%s'\n", mysql_error(maxconn));
+            }
+        }
+        mysql_close(maxconn);
+    }
+
+
+    return test.global_result;
+}