Net::HTTP#sspi_auth

# File tmp/rubies/ruby-3.2.0/lib/net/http.rb, line 1965
def sspi_auth(req)
  n = Win32::SSPI::NegotiateAuth.new
  req["Proxy-Authorization"] = "Negotiate #{n.get_initial_token}"
  # Some versions of ISA will close the connection if this isn't present.
  req["Connection"] = "Keep-Alive"
  req["Proxy-Connection"] = "Keep-Alive"
  res = transport_request(req)
  authphrase = res["Proxy-Authenticate"]  or return res
  req["Proxy-Authorization"] = "Negotiate #{n.complete_authentication(authphrase)}"
rescue => err
  raise HTTPAuthenticationError.new('HTTP authentication failed', err)
end