admin login

yes like..

<?php

$username = "admin";
$password = "password";

?>

With better username / password ofc :-P

I suppose you could, if this is just going to remain a super simple blog. You'll still want to make sure you're somehow authenticated to the site, and making authenticated requests to add, edit, or delete, maybe though the use of a cookie or something.

Of course though, you run the risk that by storing your username and password in plain text, if someone gets your source files, it could be game over. And that you have to remember to not check that file into any sort of version control. All of github is searchable, so people can just search for words like "password" and get back all the repos that have files checked in with the word "password" in them. Most often people try farming API keys this way by people who check their keys in.

I would keep your creds in a file of it's own, and include it in other files where it's needed. But since you're going to have a database anyway I assume, I'd at least considering taking the extra work to have a users table, and store your hashed password in the database, that's the safest way.