If a username and/or password is required for basic authentication and
isn't available in the configuration or connection URI, then this callback
will be invoked to obtain the username and/or password.
@param config The neo4j client configuration to update.
@param callback The callback to be invoked.
@param userdata User data that will be supplied to the callback.
@return 0 on success, or -1 on error (errno will be set).
Set the basic authentication callback.
If a username and/or password is required for basic authentication and isn't available in the configuration or connection URI, then this callback will be invoked to obtain the username and/or password.
@param config The neo4j client configuration to update. @param callback The callback to be invoked. @param userdata User data that will be supplied to the callback. @return 0 on success, or -1 on error (errno will be set).