Microsoft Windows Server 2022 supports post-handshake as default authentication 
method with TLS 1.3. It means, before we can use certificate base 
authentication with IIS and TLS 1.3 protocol, we must change default 
configuration from post-handshake authentication method to in-handshake 
authentication method. So, by default it affects all Microsoft customers who 
want to enable certificate based authentication with TLS 1.3 in IIS, because 
enabling certificate based authentication with TLS 1.3 leads us to 
err_connection_reset error.
IMHO this (post-handshake authentication method) is not correct default 
configuration in situation, where common browsers do not support post-handshake 
authentication (Firefox supports it, but it is disabled by default).

It is good to hear that post-handshake authentication method is optional and 
not preferred.

Thanks,

Urmas

From: Andrei Popov <[email protected]>
Sent: Friday, January 14, 2022 10:24 PM
To: Eric Rescorla <[email protected]>; Urmas Vanem <[email protected]>
Cc: [email protected]
Subject: RE: [EXTERNAL] Re: [TLS] TLS 1.3 and certificate based authentication

Essentially, TLS 1.3 post-handshake authentication is analogous to client auth 
via renegotiation available with TLS <= 1.2.
An important difference is that TLS 1.3 post-handshake authentication is 
optional, and major browsers chose not to support it.

In practice, this means TLS server deployments and applications that rely on 
authenticating clients post-handshake have to change if they want to enable TLS 
1.3.
These changes can include creating separate endpoints for client-authenticating 
services, and configuring those endpoints to perform client authentication 
during the handshake.

This affects a significant number of Microsoft customers, who have been using 
client auth support via renegotiation in IIS.
The typical scenario is: landing page without client authentication, then 
renegotiation with client auth if the user navigates to a protected resource on 
the page.
I recommend customers to work directly with browser vendors if they want TLS 
1.3 post-handshake auth support. This is not a TLS 1.3 standard's limitation.

Cheers,

Andrei

From: TLS <[email protected]<mailto:[email protected]>> On Behalf Of Eric 
Rescorla
Sent: Friday, January 14, 2022 9:54 AM
To: Urmas Vanem <[email protected]<mailto:[email protected]>>
Cc: [email protected]<mailto:[email protected]>
Subject: [EXTERNAL] Re: [TLS] TLS 1.3 and certificate based authentication

TLS 1.3 supports certificate-based client auth in the primary handshake.

-Ekr


On Fri, Jan 14, 2022 at 8:19 AM Urmas Vanem 
<[email protected]<mailto:[email protected]>> wrote:
Hello!

TLS 1.3 introduces post-handshake authentication. It relies on client/browser, 
client/browser must send post_handshake_auth extension to server before it can 
work. I hope I understood it correctly.
But today we know only Firefox from popular browsers support this extension 
(and not by default).

Question: How can I implement certificate based client authentication against 
web server in TLS 1.3 only environment, if browsers do not support 
post_handshake_auth extension.

I have open discussion with one big software company. Can you please share your 
opinion/recommendation here regarding to the issue?

Thanks in advance,

Urmas

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