Token service priti

Implemented Basic Token Service.. Wrote Test cases for the same.
Further extensions can be done to set session timeout period and accordingly maintain sessions. But not sure whether session timeout period is responsibility of TokenService or Log In module...
You almost never want to return the StackTrace to the client side. The stack trace exposes internal details about your code including the components that you are using. People with the wrong intent can identify the components and use publicly know vulnerabilities to exploit your application.