Solution:

<h4>Why not?
</h4>
<hr />

		<div class="challenge-wrapper">
			<form action="" method="post">
				<label>Username</label>
				<input type="text" name="username" id="cuser" placeholder="Username" class="form-control" />
				<label>Passwor</label>
				<input type="password" name="password" id="cpass" placeholder="Password" class="form-control" />
				<input type="submit" style="margin-top: 12px;" value="Login" class="form-control btn btn-success c_submit" />
			</form>
		</div>
		<div id="cresponse">
		</div>
		<script>
			// Look's like weak JavaScript auth script :)
			$(".c_submit").click(function(event) {
				event.preventDefault();
				var k = new Array(176,214,205,246,264,255,227,237,242,244,265,270,283);
				var u = $("#cuser").val();
				var p = $("#cpass").val();
				var t = true;
			
				if(u == "administrator") {
					for(i = 0; i < u.length; i++) {
						if((u.charCodeAt(i) + p.charCodeAt(i) + i * 10) != k[i]) {
							$("#cresponse").html("<div class='alert alert-danger'>Wrong password sorry.</div>");
							t = false;
							break;
						}
					}
				} else {
					$("#cresponse").html("<div class='alert alert-danger'>Wrong password sorry.</div>");
					t = false;
				}
				if(t) {
					if(document.location.href.indexOf("?p=") == -1) {
						document.location = document.location.href + "?p=" + p;
               			}
				}
			});
		</script>
		
<hr />

Reverse the password…

var u = "administrator"
var s = [];
for (i = 0; i < u.length; i++) {
	console.log(u.charCodeAt(i) - k[i] + i * 10);
	s.push(Math.abs(u.charCodeAt(i) - k[i] + i * 10));
}
var pass = ''
for (x in s) {
	pass += String.fromCharCode(s[x]);
}
console.log(pass)

user: administrator pass: OhLord4309111

Flag: FLAG-65t23674o6N2NehA44272G24