Implement JWT login route in the backend server

Some of the protected api routes will be accessible to only authorised users
express route -
**/login/gentoken/**

for now please consider only 1 user
username - testuser , password - password

once the user posts the username and password to the above route , the user will have JWT token to mark a authorized users

Start by locating the Express backend entry point and the protected API routes, then inspect how routes and request handling are organized. Exercise POST /login/gentoken/ with the specified credentials and verify that a JWT is returned for the authorized user; confirm that the result supports the intended protected-route access.

Written by the indexing model from the issue text.