def credentials(username, password, digest = false)
      self.username = username
      self.password = password
      self.digest = digest
    end
def credentials(username, password, digest = false)
      self.username = username
      self.password = password
      self.digest = digest
    end
Sets authentication credentials for a wsse:UsernameToken header.
 Also accepts whether to use WSSE digest authentication.