Openstack Paste Deploy Python paste deploy use in OpenStack

[composite:neutron]
use = egg:Paste#urlmap
/: neutronversions
/v2.0: neutronapi_v2_0

[composite:neutronapi_v2_0]
use = call:neutron.auth:pipeline_factory
noauth = extensions neutronapiapp_v2_0
keystone = authtoken keystonecontext extensions neutronapiapp_v2_0

[filter:keystonecontext]
paste.filter_factory = neutron.auth:NeutronKeystoneContext.factory

[filter:authtoken]
paste.filter_factory = keystoneclient.middleware.auth_token:filter_factory

[filter:extensions]
paste.filter_factory = neutron.api.extensions:plugin_aware_extension_middleware_factory

[app:neutronversions]
paste.app_factory = neutron.api.versions:Versions.factory

[app:neutronapiapp_v2_0]
paste.app_factory = neutron.api.v2.router:APIRouter.factory

from oslo.config import cfg
import webob.dec
import webob.exc

from neutron import context
from neutron.openstack.common import log as logging
from neutron import wsgi

LOG = logging.getLogger(__name__)



class NeutronKeystoneContext(wsgi.Middleware):
	"""Make a request context from keystone headers."""

	@webob.dec.wsgify
	def __call__(self, req):
	    # Determine the user ID
	    user_id = req.headers.get('X_USER_ID')
	    if not user_id:
	        LOG.debug(_("X_USER_ID is not found in request"))
	        return webob.exc.HTTPUnauthorized()

	    # Determine the tenant
	    tenant_id = req.headers.get('X_PROJECT_ID')

	    # Suck out the roles
	    roles = [r.strip() for r in req.headers.get('X_ROLES', '').split(',')]

	    # Human-friendly names
	    tenant_name = req.headers.get('X_PROJECT_NAME')
	    user_name = req.headers.get('X_USER_NAME')

	    # Create a context with the authentication data
	    ctx = context.Context(user_id, tenant_id, roles=roles,
	                          user_name=user_name, tenant_name=tenant_name)

	    # Inject the context...
	    req.environ['neutron.context'] = ctx

	    return self.application


def pipeline_factory(loader, global_conf, **local_conf):
	"""Create a paste pipeline based on the 'auth_strategy' config option."""
	pipeline = local_conf[cfg.CONF.auth_strategy]
	pipeline = pipeline.split()
	filters = [loader.get_filter(n) for n in pipeline[:-1]]
	app = loader.get_app(pipeline[-1])
	filters.reverse()
	for filter in filters:
	    app = filter(app)
	return app

def load_paste_app(app_name):
	"""Builds and returns a WSGI app from a paste config file.

	:param app_name: Name of the application to load
	:raises ConfigFilesNotFoundError when config file cannot be located
	:raises RuntimeError when application cannot be loaded from config file
	"""

	config_path = cfg.CONF.find_file(cfg.CONF.api_paste_config)
	if not config_path:
	    raise cfg.ConfigFilesNotFoundError(
	        config_files=[cfg.CONF.api_paste_config])
	config_path = os.path.abspath(config_path)
	LOG.info(_("Config paste file: %s"), config_path)

	try:
	    app = deploy.loadapp("config:%s" % config_path, name=app_name)
	except (LookupError, ImportError):
	    msg = (_("Unable to load %(app_name)s from "
	             "configuration file %(config_path)s.") %
	           {'app_name': app_name,
	            'config_path': config_path})
	    LOG.exception(msg)
	    raise RuntimeError(msg)
	return app