Authentication

Branch: Authentication
Feature: Service API can only be accessed by a valid token which is generated by verifying the credentials.
Functions, and files which does the same are added.
Change made.
Nesting was only done to explicitly tell whether the username or the password was missing. Combining them is also fine since we require them together.

Do you want me to implement my own find functionality ?? Cause I have used two iterators and I think using the inbuilt find() function is better than implementing own functionality.