@param prompt Prompt to be displayed.
@param buf Buffer to save the password. You should null-terminate it.
@param len Length of the buffer.
@param echo Enable or disable the echo of what you type.
@param verify Should the password be verified?
@param userdata Userdata to be passed to the callback function. Useful
for GUI applications.
@brief SSH authentication callback.
@param prompt Prompt to be displayed. @param buf Buffer to save the password. You should null-terminate it. @param len Length of the buffer. @param echo Enable or disable the echo of what you type. @param verify Should the password be verified? @param userdata Userdata to be passed to the callback function. Useful for GUI applications.
@return 0 on success, < 0 on error.