CXX-360 add support for authMechanismProperties

Our SASL implementation seems to only have support for SERVICE_NAME, so I left the others out. They are listed as "MAY IMPLEMENT" in the spec anyway.


I don't think this does what you want. Typically uassert takes a assertion code, not an ErrorCode.  You really want uassertStatusOk, but you don't have a status object. You could create one easily enough with the Status constructor though.