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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_plugin(self, service_provider=None, auth_url=None, plugins=None, **kwargs):
 """Authenticate using keystone to keystone federation. This plugin uses other v3 plugins to authenticate a user to a identity provider in order to authenticate the user to a service provider :param service_provider: service provider ID :param auth_url: Keystone auth url :param plugins: list of openstack_auth plugins to check :returns Keystone2Keystone keystone auth plugin """


        # Avoid mutable default arg for plugins
        plugins = plugins or []

        # service_provider being None prevents infinite recursion
        if utils.get_keystone_version() < 3 or not service_provider:
            return None

        keystone_idp_id = getattr(settings, 'KEYSTONE_PROVIDER_IDP_ID',
                                  'localkeystone')
        if service_provider == keystone_idp_id:
            return None

        for plugin in plugins:
            unscoped_idp_auth = plugin.get_plugin(plugins=plugins,
                                                  auth_url=auth_url, **kwargs)
            if unscoped_idp_auth:
                break
        else:
            LOG.debug('Could not find base authentication backend for '
                      'K2K plugin with the provided credentials.')
            return None

        idp_exception = None
        scoped_idp_auth = None
        unscoped_auth_ref = base.BasePlugin.get_access_info(
            self, unscoped_idp_auth)
        try:
            scoped_idp_auth, __ = self.get_project_scoped_auth(
                unscoped_idp_auth, unscoped_auth_ref,
                recent_project=kwargs['recent_project'])
        except exceptions.KeystoneAuthException as idp_excp:
            idp_exception = idp_excp

        if not scoped_idp_auth or idp_exception:
            msg = _('Identity provider authentication failed.')
            raise exceptions.KeystoneAuthException(msg)

        session = utils.get_session()

        if scoped_idp_auth.get_sp_auth_url(session, service_provider) is None:
            msg = _('Could not find service provider ID on keystone.')
            raise exceptions.KeystoneAuthException(msg)

        unscoped_auth = v3_auth.Keystone2Keystone(
            base_plugin=scoped_idp_auth,
            service_provider=service_provider)
        return unscoped_auth