Protect cached username, password and token on client

Protect cached username, password and token on client

Keep the memory segment containing username and password in
"struct user_pass" encrypted. Works only on Windows.

Username and auth-token cached by the server are not covered
here.

v2: Encrypt username and password separately as it looks more
robust. We continue to depend on the username and password buffer
sizes to be a multiple of CRYPTPROTECTMEMORY_BLOCK_SIZE = 16,
which is the case now. An error is logged if this is not the case.

v3: move up ASSERT in auth_token.c

Change-Id: I42e17e09a02f01aedadc2b03f9527967f6e1e8ff
Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20240906112908.1009-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg29079.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 12a9c357b6a7b55bea929eb5d9669e6386ab0d0e)