I'm curious to know how ifttt.com authenticate a supplied WordPress admin login credentials. And after authorization is granted, how does it publish post on our behalf? am curious to know what communication protocol it is using.
IFTTT.com connects to your WordPress site via XML-RPC, as the dudes at wpbeginner.com already found out:
Go to IFTTT and create your account. IFTTT works with all WordPress.org self-hosted blogs (version 3.x and above) and WordPress.com blogs as well. You MUST have XML-RPC enabled to work with IFTTT.