Add schannel to integration tests

[raycoll]

Problem:

s2n is deployed in environments where the clients and servers it interacts with may be running on Windows using the schannel TLS library. Implementation updates to either schannel or s2n can cause compatibility issues.

Solution:

Add schannel coverage to s2n's integration test suite.

• Does this change what S2N sends over the wire? No.
• Does this change any public APIs? No
• Which versions of TLS will this impact? All.

Requirements / Acceptance Criteria:

• Will the Usage Guide or other documentation need to be updated? N/A
• Testing: Update integration tests to cover windows schannel clients. Ideally windows10 and 11(not sure if the schannel version is pinned to windows version).
  • Will this change trigger SAW changes? No
  • Should this change be fuzz tested? No

[goatgoose]

We agree that adding an integration test for schannel would be beneficial. However, I think we can only run schannel on windows. This is an issue because our integration tests are setup to all run locally on the same machine, and we currently can't build s2n-tls on windows: #497.

So, we do want to add a test for this but it might be more involved than just adding a normal client to our existing integration test setup.