The oracle machine can initiate a request to the data source whose URL is the HTTP link address. How does the oracle machine determine whether the HTTP request has been attacked by a man-in-the-middle, such as whether the returned result has been tampered with by a man-in-the-middle? Hope you can help me! Thanks!
Depending on the oracle implementation, they may have various levels of protection, https being the topmost. But in the end, it's typically not really their job to be 100% certain of the data authenticity, since they also have no idea what the real data should be if you just give them an arbitrary URL to get data from.
So an oracle just gets the data from the URL you give it to, and that's it. It's up to you to decide whether the data is reliable. That's why an oracle is a big(?) security issue in any architecture. Chainlink has various means to remedy this problem, mostly by utilizing multiple oracles and comparing their results.