We shall only register auth schemes Basic, Digest, NTLM which settings.xml supports. Other aren't really supported. More over, the SPNEGO support in HttpClient is broken and shall not be used: HTTPCLIENT-1625 and HTTPCLIENT-1938.
is depended upon by
WAGON-538Basic authentication fails if the password contains non-ASCII characters
WAGON-540Switch to modern-day encoding (UTF-8) of auth credentials