This is a TLS server using a vendored fork of the Go TLS stack that has renegotation indication extension forcibly disabled, which will trigger CVE-2009-3555 mitigations in OpenSSL 3.0+. Note that it isn't truly vulnerable to CVE-2009-3555 because the Go TLS stack doesn't allow renegotiations at all.
The function of this program is to act as a test server for TLS clients that refuse to connect to servers with insecure client renegotiation configurations, like OpenSSL 3.0+ without the SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION option.