Function sudoku_backend::ops::routes::v1::auth::login

pub fn login(
    db: DatabaseConnection, 
    ac: State<ActivityCache>, 
    cookies: Cookies, 
    form: Form<LoginForm>
) -> Result<Result<Custom<Json<SanitisedUserData>>, Custom<Json<LoginError>>>, Custom<Json<GenericError>>>

Log the user in.

Check the received form. If login exists and password verifies correct and not a dupe, update session to reflect permissions.