Part 3: Sign-up form

The idea is the same as part 2. Students must:

• Have a form that contains at least 2 input fields: username and password.
• The error message or success message are hidden before the user click submit buttons.
• You should apply some rules for the format of either username or password.
  • You can search google for the pattern youd like to have on your website
  • User preg_match() function to match the pattern and the form data
• There should be messages:
  • Error message for empty field.
  • Error message if there is invalid username/password
  • If there is no error, display a success message saying that the user signed up successfully.
• If the new account is valid, append the new account to the database:
  • Read the json file and decode to an associative array.
  • Use function array_push() to append the new account to the array. NOTE: the new account should be in a small array with the same structure as the decoded array.
  • Use function file_put_contents() to write the new json string into the original file.