Login functionality added

backend/login.php

+<?php
+include_once("database.php");
+$postData = file_get_contents("php://input");
+$request = json_decode($postData);
+
+if (isset($postData) && !empty($postData)) {
+
+    $pwd = mysqli_real_escape_string($mysqli, trim($request->password));
+    $username = mysqli_real_escape_string($mysqli, trim($request->username));
+    $sql = "SELECT * FROM users where username='$username'";
+
+    if ($result = mysqli_query($mysqli, $sql)) {
+        while ($row = mysqli_fetch_assoc($result)) {
+            if (password_verify($pwd, $row['password'])) {
+                echo json_encode($row);
+                exit;
+            }
+        }
+    }
+
+    http_response_code(404);
+}