'Create a signed jwt.
Args:
http: unused
additional_claims: dict, additional claims to add to
the payload of the JWT.
Returns:
An AccessTokenInfo with the signed jwt'

def get_access_token(self, http=None, additional_claims=None):

    if (additional_claims is None):
        if ((self.access_token is None) or self.access_token_expired):
            self.refresh(None)
        return client.AccessTokenInfo(access_token=self.access_token, expires_in=self._expires_in())
    else:
        (token, unused_expiry) = self._create_token(additional_claims)
        return client.AccessTokenInfo(access_token=token, expires_in=self._MAX_TOKEN_LIFETIME_SECS)
