There's no official API to get a Russian equivalent of ITIN (also known as INN or ИНН in Russian) by the person's passport data although there are the government official sites that provide such information through a form requiring no authorization. Unfortunately, 3rd-party services like DaData don't provide this information either.

So, if you want to ease your clients' pain of, let's say, filling in a declaration, you'll have to use one of those forms manually OR use this little lib for automation.

For the reasons mentioned above, this lib is not guaranteed to work reliably. Use it on your own risk and responsibility.