Refactor the SP metadata loading logic.

The SP metadata get loaded once at the start from all sources to
index the entities ids and where the come from.

Upon every request from an SP, the metadata of that SP gets reloaded
from the last known source: if it's not there anymore the server
tries to look in all known sources again.

Protip! Using:
```
metadata:
    local:
        - conf/*.xml
```

Allows to drop config files to the directory at runtime and have their
configuration picked up without restarting the server.

Other goodies:
* Invalid SP metadata are logged and discarded, but no longer prevent
  the rest of metadata from loading. (Fix #210)
* Duplicate entityIds are discarded with precedence given to local
  sources (local > db > remote) (Fix #205).
* Display the source of the SP metadata in the UI

templates/home.html

@@ -10,11 +10,14 @@ <h3 class="border-bottom mt-2 mb-2 border-italia">Service Provider configurati</
       <tbody>
         {% for item in sp_list %}
             <tr>
-                <td >
-                   {{ item['entityID'] }}
+                <td>
+                    {{ item['entityID'] }}
+                    <small class="float-right">
+                        <mark>loaded from {{ item['location'] }}</mark>
+                    </small>
                 </td>
            </tr>
         {% endfor %}
       </tbody>
     </table>
-{% endblock %}
+{% endblock %}

testenv/server.py

@@ -284,7 +284,7 @@ def _handle_http_post(self, action):
 
     def _get_certificates_by_issuer(self, issuer):
         try:
-            return self._registry.get(issuer).certs()
+            return self._registry.load(issuer).certs()
         except KeyError:
             self._raise_error(
                 'entity ID {} non registrato, impossibile ricavare'
@@ -357,7 +357,7 @@ def users(self):
                 'primary_attributes': spid_main_fields,
                 'secondary_attributes': spid_secondary_fields,
                 'users': self.user_manager.all(),
-                'sp_list': self._registry.all(),
+                'sp_list': self._registry.load_all().keys(),
                 'can_add_user': can_add_user
             }
         )
@@ -393,8 +393,9 @@ def index(self):
             **{
                 'sp_list': [
                     {
-                        "entityID": sp
-                    } for sp in self._registry.all()
+                        "entityID": entity_id,
+                        "location": sp_metadata.location,
+                    } for (entity_id, sp_metadata) in self._registry.load_all().items()
                 ],
             }
         )
@@ -405,7 +406,7 @@ def get_destination(self, req, sp_id):
         acs_index = getattr(req, 'assertion_consumer_service_index', None)
         protocol_binding = getattr(req, 'protocol_binding', None)
         if acs_index is not None:
-            acss = self._registry.get(
+            acss = self._registry.load(
                 sp_id).assertion_consumer_service(index=acs_index)
             if acss:
                 destination = acss[0].get('Location')
@@ -590,7 +591,7 @@ def login(self):
                                 atcs_idx
                             )
                         )
-                        sp_metadata = self._registry.get(sp_id)
+                        sp_metadata = self._registry.load(sp_id)
                         required = []
                         optional = []
                         if atcs_idx and sp_metadata:
@@ -791,7 +792,7 @@ def continue_response(self):
     def _sp_single_logout_service(self, issuer_name):
         _slo = None
         try:
-            _slo = self._registry.get(issuer_name).single_logout_services[0]
+            _slo = self._registry.load(issuer_name).single_logout_services[0]
         except Exception:
             pass
         return _slo