Bug#33520778 compiler warnings in authentication_win

Issue
=====

clang on windows reports:

libmysql/authentication_win/common.h(169,41):
warning: cast from 'const char *' to 'unsigned char *' drops const
qualifier [-Wcast-qual]
  Blob(const char *str) : m_ptr((byte *)str) { m_len = strlen(str); }

libmysql/authentication_win/plugin_client.cc(64,30):
warning: missing field 'authenticate_user_nonblocking' initializer
[-Wmissing-field-initializers]
    win_auth_handshake_client};

libmysql/authentication_win/handshake.cc(57,25):
warning: cast from 'const char *' to 'char *' drops const qualifier
[-Wcast-qual]
      NULL, (SEC_CHAR *)ssp,

libmysql/authentication_win/handshake_client.cc(183,17):
warning: variable 'saved_byte' may be uninitialized when used here
[-Wconditional-uninitialized]
    data[254] = saved_byte;

Change
======

- reinterpret_cast<...>(byte) instead of c-style cast
- set authenticate_user_nonblocking in win_auth_client_plugin to 0
- const_cast<SEC_CHAR *>
- initialize saved_byte

RB: 27204

Author: weigon

libmysql/authentication_win/common.h

@@ -166,7 +166,10 @@ class Blob {
   Blob(const byte *ptr, const size_t len)
       : m_ptr(const_cast<byte *>(ptr)), m_len(len) {}
 
-  Blob(const char *str) : m_ptr((byte *)str) { m_len = strlen(str); }
+  Blob(const char *str)
+      : m_ptr(const_cast<byte *>(reinterpret_cast<const byte *>(str))) {
+    m_len = strlen(str);
+  }
 
   byte *ptr() const { return m_ptr; }
 

libmysql/authentication_win/handshake.cc

@@ -54,7 +54,7 @@ Handshake::Handshake(const char *ssp, side_t side)
   // Obtain credentials for the authentication handshake.
 
   ret = AcquireCredentialsHandle(
-      NULL, (SEC_CHAR *)ssp,
+      NULL, const_cast<SEC_CHAR *>(ssp),
       side == SERVER ? SECPKG_CRED_INBOUND : SECPKG_CRED_OUTBOUND, NULL, NULL,
       NULL, NULL, &m_cred, &m_expire);
 

libmysql/authentication_win/handshake_client.cc

@@ -139,8 +139,8 @@ int Handshake_client::write_packet(Blob &data) {
       which can be used to allocate buffer of appropriate size.
   */
 
-  size_t len2 = 0;  // length of the second part of first data payload
-  byte saved_byte;  // for saving byte 255 in which data length is stored
+  size_t len2 = 0;      // length of the second part of first data payload
+  byte saved_byte = 0;  // for saving byte 255 in which data length is stored
 
   if (m_round == 1 && data.len() > 254) {
     len2 = data.len() - 254;

libmysql/authentication_win/plugin_client.cc

@@ -61,4 +61,5 @@ extern "C" auth_plugin_t win_auth_client_plugin = {
     win_auth_client_plugin_deinit,
     NULL,  // option handling
     NULL,
-    win_auth_handshake_client};
+    win_auth_handshake_client,
+    nullptr};