Group add user workflow (invitation) with configurable intermediary pending/accept membership status

Problem
Currently, when adding a member to a group the user gains the membership immediately. Optionally, an email is sent to the user, but this can be skipped by the coach/owner of the group. In the worst case the user does not notice that he was put into a group. From the perspective of data privacy protection laws this can be critical.

Solution
The system can be configured to force two workflows:

• Force a pending state instead of immediate membership. Users have to accept the membership explicitly.
• Force the sending of the notification email instead of making it optional

The default configuration is made in the olat.properties file and can be different for users with the different roles (users/authors/user workflows etc). As the base infrastructure the datamodel developed for the payment module is extended. System administrators can configure the settings in the system admin tab in the group module configuration.

The pending membership is displayed in the user management of the group together with the state of the invitation. Group coaches/owners can delete a pending invitation.

Pending memberships count as full group memberships regarding the number of available seats in a group. When a group has 5 available seats and 3 users have been invited but are still in pending state, the group as 0 real members, 3 pending invitations and the remaining seats e.g. for self registration is calculated as 2.

When doing a self registration this process is skipped, users are members immediately.

Removing a user from a group is an immediate action, no accept workflow is triggers. However, the sending of the email can be forced depending of the system configuration (see above).

Config options

# Behavior when manually adding a user to a group. There are two workflow elements regarding data privacy 
# that can be configured:
# a) Email notification: is the notification email about the new group membership mandatory or optional? 
#    Default is true for normal users and optional for users with role author, usermanager, groupmanager or administrator
group.mandatory.enrolment.email.users=true
group.mandatory.enrolment.email.authors=false
group.mandatory.enrolment.email.usermanagers=false
group.mandatory.enrolment.email.groupmanagers=false
group.mandatory.enrolment.email.administrators=false
# b) Invitation only or direct membership: is the new group membership immediate or is it only an invitation 
#    that must be accepted by the invited user? 
#    Default is invitation-only for normal users and immediate group membership without the need to accept
#    for users with the role author, usermanager, groupmanager or administrator
group.accept.membership.users=true
group.accept.membership.authors=false
group.accept.membership.usermanagers=false
group.accept.membership.groupmanagers=false
group.accept.membership.administrators=false