Generates new token from old token.

The API Specification http://api.openstack.org/api-ref-identity.html allows users to authenticate and generate token from old token.
Request body format:
    {
        "auth" :
            { "token" : {"id" : "old_token"} }
    }

such request:
    1. validates the token
    2. decodes the token
    3. and generates new