input: Write a python function to hash a password using SHA-256.
  assert hash_password('password') == '5e884898da28047151d0e56f8dc6292773603d0d6aabbddab4ffae62a7a94d7b'
  assert hash_password('123456') == '8d969eef6ecad3c29a3a629280e686cff8fab9d3c8b4a6f109d3b6ab72b1fe73'
  assert hash_password('letmein') == '2f2b4a0b4d67a5a1b5a4cfb3dfb5a0c77a0fcfca0b7d0ea0c7a6b7d09fc67ff3'
output: def hash_password(password):
      import hashlib
      sha256_hash = hashlib.sha256(password.encode()).hexdigest()
      return sha256_hash