Use of secrets module instead of random module

[sanket1729]

The use of random is not recommended for cryptographic or security purposes.

Warning The pseudo-random generators of this module should not be used for security purposes. For security or cryptographic uses, see the secrets module.

Reference: https://docs.python.org/3/library/random.html (Red Box warning)

If the project wants to use random for legacy reasons, it should atleast be mentioned that it is insecure. If this is mentioned elsewhere in the book, please close the issue.