Allow choosing a saml entityid

Allows you to pick an entityid when using federation XML data or an MDQ with many entries.  Pysaml2's MDQ metadata is loaded lazily, after you provide a key, so it's necessary to pass the entityid as a key

gluon/contrib/login_methods/saml2_auth.py

@@ -104,11 +104,12 @@ def obj2dict(obj, processed=None):
                                     types.BuiltinFunctionType,
                                     types.BuiltinMethodType))
 
-def saml2_handler(session, request, config_filename = None):
+def saml2_handler(session, request, config_filename = None, entityid = None):
     config_filename = config_filename or os.path.join(request.folder,'private','sp_conf')
     client = Saml2Client(config_file = config_filename)
-    idps = client.metadata.with_descriptor("idpsso")
-    entityid = idps.keys()[0]
+    if not entityid:
+    	idps = client.metadata.with_descriptor("idpsso")
+    	entityid = idps.keys()[0]
     bindings = [BINDING_HTTP_REDIRECT, BINDING_HTTP_POST]
     binding, destination = client.pick_binding(
         "single_sign_on_service", bindings, "idpsso", entity_id=entityid)
@@ -145,7 +146,7 @@ class Saml2Auth(object):
             username=lambda v:v['http://schemas.xmlsoap.org/ws/2005/05/identity/claims/upn'][0],
             email=lambda v:v['http://schemas.xmlsoap.org/ws/2005/05/identity/claims/upn'][0],
             user_id=lambda v:v['http://schemas.xmlsoap.org/ws/2005/05/identity/claims/upn'][0],
-            ), logout_url=None, change_password_url=None):
+            ), logout_url=None, change_password_url=None, entityid=None):
         self.config_file = config_file
         self.maps = maps
 
@@ -154,9 +155,12 @@ class Saml2Auth(object):
 
         # URL to let users change their password in the IDP system
         self.saml_change_password_url = change_password_url
+	
+	# URL to specify an IDP if using federation metadata or an MDQ
+	self.entityid = entityid
 
     def login_url(self, next="/"):
-        d = saml2_handler(current.session, current.request)
+        d = saml2_handler(current.session, current.request, entityid=self.entityid)
         if 'url' in d:
             redirect(d['url'])
         elif 'error' in d: