'Add new entries to the \'links\' subdictionary in the response.
Adds \'identity_provider\' key with URL pointing to related identity
provider as a value.
:param ref: response dictionary'

@classmethod
def _add_related_links(cls, context, ref):

    ref.setdefault('links', {})
    base_path = '/'.join([IdentityProvider.base_url(context), ref['idp_id']])
    ref['links']['identity_provider'] = base_path
