Endpoints for GUIs to handle OCM invites

[glpatcern]

Posting here for further reference a summary of the envisioned endpoints to implement a GUI for OCM invites, which were discussed in Gitter by @michielbdejong.

The scope was the implementation in Nextcloud, however the discussion is generic and applicable to all EFSSs. In fact, these ideas were originally presented at CS3 2023 in Barcelona by Elizaveta Ragozina.

1. GUI for invite sender to create an invite. This can then be:

• sent out via email, or
• presented as a WAYF URL for copying onto the clipboard
• presented as an invite string of the form ocm-invite://<token>@<sending-host> for copying onto the clipboard
• The email may contain a combination of the following:
  • a link for publicly accessing the resource without doing any OCM at all (standard 'share via email'). Not part of the invite flow.
  • an invite string of the form ocm-invite://<token>@<sending-host>
  • a link to a WAYF page

2. On the public view page there may be:
   • an 'add this resource to my cloud' button, where the recipient may enter their OCM address (see section '3.3 public link flow' of https://datatracker.ietf.org/doc/draft-lopresti-open-cloud-mesh/). Also not part of the invite flow. Such a link may also exist on a page that does not itself display the resource (section '3.4 public invite flow')
   • a way to initiate the invite flow, by either generating or pasting an invite string of the form ocm-invite://<token>@<sending-host> (not implemented or documented, just an idea)
3. The WAYF page does not need to be part of the EFSS. It can be hosted by EOSC, for instance. It would redirect the user to their own OCM-capable server, with the invite string in the query parameter of the URL (this is what ScienceMesh does, but I think we didn't document this in the OCM spec)
4. The EFSS should have an endpoint where it receives the redirect from the WAYF server.
5. A GUI where the user can paste an invite string of the form ocm-invite://<token>@<sending-host>
6. A GUI where the user can see an overview of sent/received pending/accepted invites
7. A backchannel endpoint for section '3.5.2. Invite Acceptance Request Details' of https://datatracker.ietf.org/doc/draft-lopresti-open-cloud-mesh/

[michielbdejong]

Proposal to standardise the hyperlink format for going from step 3 to step 4: #163