CORSの原理を知って正しく使おう

Recently, there has been a surge in questions about CORS (Cross-Origin Resource Sharing) on ​​Q&A sites and the like, but many of these questions seem to be asking for ways to circumvent CORS restrictions without any understanding of the principles of CORS. However, because CORS is a browser security feature, simply trying to get something to "just work" without understanding the principles can lead to serious vulnerabilities. This video explains the principles of CORS, focusing in particular on "why CORS works the way it does."