Convert emails to lowercase when storing

And db migration sql to convert existing addresses.

synapse/handlers/auth.py

@@ -611,6 +611,18 @@ class AuthHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def add_threepid(self, user_id, medium, address, validated_at):
+        # 'Canonicalise' email addresses down to lower case.
+        # We've now moving towards the Home Server being the entity that
+        # is responsible for validating threepids used for resetting passwords
+        # on accounts, so in future Synapse will gain knowledge of specific
+        # types (mediums) of threepid. For now, we still use the existing
+        # infrastructure, but this is the start of synapse gaining knowledge
+        # of specific types of threepid (and fixes the fact that checking
+        # for the presenc eof an email address during password reset was
+        # case sensitive).
+        if medium == 'email':
+            address = address.lower()
+
         yield self.store.user_add_threepid(
             user_id, medium, address, validated_at,
             self.hs.get_clock().time_msec()

synapse/storage/schema/delta/36/user_threepids.sql

@@ -13,4 +13,11 @@
  * limitations under the License.
  */
 
-CREATE INDEX user_threepids_medium_address on user_threepids (medium, LOWER(address));
+/*
+ * Update any email addresses that were stored with mixed case into all
+ * lowercase
+ */
+UPDATE user_threepids SET address = LOWER(address) where medium = 'email';
+
+/* Add an index for the select we do on passwored reset */
+CREATE INDEX user_threepids_medium_address on user_threepids (medium, address);