Adding TOTP_ISSUER as settings value

Using the site name at this point doesn't always make sense. This gives you the possibility to set TOTP_ISSUER in the settings.py file and show this information in the TOTP app.

two_factor/views/core.py

@@ -707,6 +707,8 @@ class QRGeneratorView(View):
     }
 
     def get_issuer(self):
+        if settings.TOTP_ISSUER:
+            return settings.TOTP_ISSUER
         return get_current_site(self.request).name
 
     def get_username(self):