Decrypting HLS stream keys on the fly according to https://blog.jonlu.ca/posts/illegal-streams

decrypt-fetch.js

(function() {
      const originalFetch = window.fetch;
      window.fetch = function(input, init){
          if(init && init.method === 'GET' && input.indexOf("something.com/aes") !== -1) {
              const rewrittenUrl = "https://example.com/key.php?key="+input;
              init = { ...init, url: rewrittenUrl };
              const modifiedRequest = new Request(rewrittenUrl, init);
              return originalFetch.call(this, modifiedRequest);
          }
          return originalFetch.call(this, input, init);
      };
  })();

decrypt-xhr.js

(function (open) {
	XMLHttpRequest.prototype.open = function (method, url, async, user, pass) {
		var rewrittenUrl = url;
		if(url.indexOf("svcs.mlb")!=-1){
			rewrittenUrl="https://example.com/key.php?id=keyURL";
		}
		if(url.indexOf("svcs.plus.espn")!=-1){
			rewrittenUrl="https://example.com/key.php?id=keyURL";
		}
		open.call(this, method, rewrittenUrl, async, user, pass);
	};
})(XMLHttpRequest.prototype.open);