def string_cache_key_adapter(obj):
    """Cache key adapter for string value

    >>> from pyramid.testing import setUp, tearDown
    >>> config = setUp()

    >>> from pyams_utils.interfaces import ICacheKeyValue
    >>> from pyams_utils.cache import string_cache_key_adapter
    >>> config.registry.registerAdapter(string_cache_key_adapter, (str, ), ICacheKeyValue)

    >>> value = 'my test string'
    >>> key = ICacheKeyValue(value)
    >>> key == value
    True

    >>> tearDown()
    """
    return obj