Explicitly adding channel bindings on the client

[inejge]

In the current API I see no way to add channel bindings to an Ntlm context when authenticating a client. (Motivation: AD can be configured to refuse authentication from an LDAP client doing an NTLM bind over a TLS connection if the channel bindings AvP is not supplied.)

Adding a method to Ntlm which sets the channel_bindings field to the supplied ChannelBindings struct does the right thing protocol-wise, i.e., the channel bindings AvP is correctly calculated and added to the AUTHENTICATE message. Would a PR with this kind of addition be appropriate, or is there another preferred way to add this functionality to the library?

[CBenoit]

Hi!

PRs are absolutely welcomed, and encouraged!!

About the suggested change, however, my guess is that it was not intended for the channel_bindings field to be overridden by the user, as-is. It is already set internally in some code paths for NTML challenge and NTLM authenticate:

sspi-rs/src/ntlm/mod.rs

Line 275 in 55ae932

self.channel_bindings = Some(ChannelBindings::from_bytes(&sec_buffer.buffer)?);

If we add a method to set the channel_bindings, it’s likely we should carefully consider the various new interactions.

Since I’m not the most familiar with NTLM, I’ll cc other people: Pavlo Myroniuk (@TheBestTvarynka) Alex Yusiuk (@RRRadicalEdward)

[inejge]

I believe that the quoted line is meant to be executed on the server when accepting the security context sent from the client. So, the channel bindings must have been already supplied by the client -- for which the current API lacks the method, hence my inquiry. But of course, let the other contributors chime in.

[awakecoding]

For reference on channel bindings in the SSPI API just search "channel_bindings" in the FreeRDP source code: https://github.com/search?q=repo%3AFreeRDP%2FFreeRDP%20channel_bindings&type=code

I had forgotten that detail, but it looks like the channel binding is passed through an SSPI input buffer of type SECBUFFER_CHANNEL_BINDINGS.

However, I suppose you want a Rust API as well?

[inejge]

I would like to have the rough equivalent of the chan_bindings parameter to gss_init_sec_context() in GSSAPI (RFC 2743), which lets one specify the channel bindings when initializing the security context on the client side. In sspi::Ntlm, it could be part of the security context builder chain, or a separate method. (Those with a better understanding of the crate's structure would be best placed to decide.)