def METHOD_NAME(self, config):
    """Create a generator function for generating ``token`` value. This
    method will create a Bearer Token generator with
    :class:`authlib.oauth2.rfc6750.BearerToken`.
    Configurable settings:
    1. OAUTH2_ACCESS_TOKEN_GENERATOR: Boolean or import string, default is True.
    2. OAUTH2_REFRESH_TOKEN_GENERATOR: Boolean or import string, default is False.
    3. OAUTH2_TOKEN_EXPIRES_IN: Dict or import string, default is None.
    By default, it will not generate ``refresh_token``, which can be turn on by
    configure ``OAUTH2_REFRESH_TOKEN_GENERATOR``.
    Here are some examples of the token generator::
        OAUTH2_ACCESS_TOKEN_GENERATOR = 'your_project.generators.gen_token'
        # and in module `your_project.generators`, you can define:
        def gen_token(client, grant_type, user, scope):
            # generate token according to these parameters
            token = create_random_token()
            return f'{client.id}-{user.id}-{token}'
    Here is an example of ``OAUTH2_TOKEN_EXPIRES_IN``::
        OAUTH2_TOKEN_EXPIRES_IN = {
            'authorization_code': 864000,
            'urn:ietf:params:oauth:grant-type:jwt-bearer': 3600,
        }
    """
    conf = config.get('OAUTH2_ACCESS_TOKEN_GENERATOR', True)
    access_token_generator = create_token_generator(conf, 42)
    conf = config.get('OAUTH2_REFRESH_TOKEN_GENERATOR', False)
    refresh_token_generator = create_token_generator(conf, 48)
    expires_conf = config.get('OAUTH2_TOKEN_EXPIRES_IN')
    expires_generator = create_token_expires_in_generator(expires_conf)
    return BearerTokenGenerator(
        access_token_generator,
        refresh_token_generator,
        expires_generator
    )