Invite links do not assign any channel or username on user registration

Description:

When inviting new users to a rocketchat instance , the user that is created gets:

• No username set
• No default channel assigned
• The channel where the invite link was generated is not assigned either

Without username it seems that the user cannot login and gets a "user blocked" error.

If I set the username afterwards manually, the user can login but is then not invited in the intended channel nor in the default channels.

Steps to reproduce:

1. Generate invite link in any existing channel
2. Give the link to somebody, have them register a new user account
3. Attempt to log in

Expected behavior:

Users should be able to log in, granted access to the default channels and the channel where the invite link was generated.

Actual behavior:

Users can't login.

Server Setup Information:

• Version of Rocket.Chat Server: 3.5.0
• Operating System: CentOS 7
• Deployment Method: docker compose
• Number of Running Instances: 1
• DB Replicaset Oplog: enabled
• NodeJS Version: v12.16.1
• MongoDB Version: v4.2.8

Client Setup Information

• Desktop App or Browser Version: Any client or web browser
• Operating System: Any OS

Additional context

Our Instance is set up with new user registration disabled (in order to only allow registration through invites).

Reproduce the issue using the listed invite-link registration steps with registration disabled, then trace the registration flow for invite-created users. Confirm the resulting account receives a username, can log in, and is added to both default channels and the channel associated with the invite link.