Can now have multiple system actors

We also handle webfinger/activity serialization properly

api/funkwhale_api/federation/authentication.py

@@ -0,0 +1,46 @@
+import cryptography
+
+from django.contrib.auth.models import AnonymousUser
+
+from rest_framework import authentication
+from rest_framework import exceptions
+
+from . import actors
+from . import keys
+from . import serializers
+from . import signing
+
+
+class SignatureAuthentication(authentication.BaseAuthentication):
+    def authenticate(self, request):
+        try:
+            signature = request.META['headers']['Signature']
+            key_id = keys.get_key_id_from_signature_header(signature)
+        except KeyError:
+            raise exceptions.AuthenticationFailed('No signature')
+        except ValueError as e:
+            raise exceptions.AuthenticationFailed(str(e))
+
+        try:
+            actor_data = actors.get_actor_data(key_id)
+        except Exception as e:
+            raise exceptions.AuthenticationFailed(str(e))
+
+        try:
+            public_key = actor_data['publicKey']['publicKeyPem']
+        except KeyError:
+            raise exceptions.AuthenticationFailed('No public key found')
+
+        serializer = serializers.ActorSerializer(data=actor_data)
+        if not serializer.is_valid():
+            raise exceptions.AuthenticationFailed('Invalid actor payload')
+
+        try:
+            signing.verify_django(request, public_key.encode('utf-8'))
+        except cryptography.exceptions.InvalidSignature:
+            raise exceptions.AuthenticationFailed('Invalid signature')
+
+        user = AnonymousUser()
+        ac = serializer.build()
+        setattr(request, 'actor', ac)
+        return (user, None)