python3: ascii-encode saml provider id before hashing it (#31183)

src/authentic2/saml/models.py

@@ -335,7 +335,8 @@ class LibertyProvider(Service):
     def save(self, *args, **kwargs):
         '''Update the SHA1 hash of the entity_id when saving'''
         if self.protocol_conformance == 3:
-            self.entity_id_sha1 = hashlib.sha1(self.entity_id).hexdigest()
+            self.entity_id_sha1 = hashlib.sha1(self.entity_id.encode('ascii')) \
+                    .hexdigest()
         super(LibertyProvider, self).save(*args, **kwargs)
 
     def clean(self):