def _get_token(self, type, data, expiration):
"""
Generate new token if:
1. first time 2. previous token is expired
Otherwise get token from cache.
"""
s = Serializer(current_app.config['SECRET_KEY'], expiration)
cached_token = _token_cache.get((self, type))
header = s.make_header({})
if cached_token and header['exp'] >= s.now():
return cached_token
token = s.dumps(data)
_token_cache[(self, type)] = token
return token
