Federation: joining a circle account confusion

This is a slightly obscure bug with joining federated public circles

  1. I logged into any user from api.test-paris.happy-dev.fr in one tab
  2. I then logged into a user on api.test2.startinblox.com user, which has the same username as ANY user from test-paris
  3. When I click join circle the user with the same name is submitted to the server successfully Screenshot_2020-03-17_at_19.44.58 Screenshot_2020-03-17_at_19.47.55 Screenshot_2020-03-17_at_19.44.45

Here's the HTML for the sib-form ("Join Circle") Screenshot_2020-03-18_at_11.10.55 I believe the user's webid is bound to the request with hd-inherit-bind-user2input="input[name='user.@id']". Note that I'm not authenticated with this user in any tab

@jbpasquier @matthieu