Removing Extensions from Client Hello Header

[Benjamin Kaduk]

On Mon, Nov 11, 2019 at 12:32:22PM -0700, Phil Neumiller wrote:
> I am speaking TLS 1.3 with openssl to a hardware device that I can't change. 
> I need the client hello header to only support certain  extensions, yet I
> see no way in the SSL API to remove the default extensions in the TLS 1.3
> client hello.  Can I clear them all and just add the ones I want?  What am I
> missing?  Do I have to modify the SSL code to do this?  It seems like there
> should be an orthodox way to do this.

You have to disable them one by one; see SSL_CTX_set_options(3) and (e.g.)
SSL_OP_NO_EXTENDED_MASTER_SECRET.

-Ben