The authentication method. Must match the member set in data; unset fails with E_INVALIDARG. For user name and password use AUTH_DATA_TYPE_CREDENTIALS.Values: AUTH_DATA_TYPE_UNDEFINED (0), AUTH_DATA_TYPE_MFILES_LEG1 (1), AUTH_DATA_TYPE_MFILES_LEG2 (2), AUTH_DATA_TYPE_WINDOWS (3), AUTH_DATA_TYPE_PLUGIN (4), AUTH_DATA_TYPE_CREDENTIALS (5), AUTH_DATA_TYPE_ANONYMOUS (6).