Until this moment, there is still no button for giveaway sharing. This is because I thought that someone can just brute force giveaways from inline_mode.
Right now I decided to make additional security code for giveaway sharing. It will be generated randomly with giveaway and inline request will look like: 0_{id}_aOp3xz.
The code (last part of command) may contain symbols 0-9, a-z, A-Z and total it can be like (10+52) ^ 5 = 916132832 combinations, so brute force is useless.