The intention of this module is to replace and drastically improve the invitation system that comes with OG; which is lacking in functionality and usability. This module was created in response to a discussion at #318082: Issues Problems with Invitations, Group Types, Access, etc...
The normal OG invitation system sends an email to the list of users supplied, providing them with a message about joining and a simple link to the group home page. This presents a number of issues, for example, if the given group is a private group, in which the invitee will land on an Access Denied page. Another flawed example is if a group admin invites a user to a moderated group, which in turn, results in the invitee having to request membership, which then leads to the admin having to approve an invitation that he/she just sent out.
OG Invite Link overrides the user invitation form that comes with OG - used to invite non-members to a given group. The key difference is that invitation emails contains a special tokenized invitation link, meant specifically for that user. Each invitation is also stored and tracked inside the database. When following the tokenized invitation link, the user is either automatically enrolled in the given group, if the group is open, or membership is automatically requested, if the group is moderated or invite-only. If a group admin sends out an invitation, the invitee is automatically enrolled regardless of the group type. If in the event that membership is requested through a followed invitation, the user is redirected elsewhere and notifying about the event, to avoid any access issues which might occur by being redirected to the group. Another interesting feature is that if a user follows their invitation link from an email and is not logged in, they will be logged into their account automatically, which avoids lost invitation links caused by rerouted logins.
The access control and workflow for group invitations is as follow (depending on the group selectivity option):
Open: Any group members can invite. Invitations will auto-join the user without approval.
Moderated: Any group members can invite. Invitations will have to be approved by the admin. Admin-sent invitations will automatically be approved.
Invite only: Any group members can invite. Invitations will have to be approved by the admin. Admin-sent invitations will automatically be approved.
Closed: Only admin can invite users. Admin-sent invitations will automatically be approved.