Allow email subscription to a category/meeting

[paulmillar]

Is your feature request related to a problem? Please describe.

When advocating for a group to use Indico for managing meetings, one feedback was that Indico doesn't support calendar synchronisation in the same way they were used to.

Currently, calendar synchronisation is achieved via email. When a meeting is organised, an email is sent (automatically) to the invited people, with a machine-readable description of the meeting. Certain email clients (if so configured) will react to these invitation emails by adding corresponding entries in the user's calendar (perhaps only after the user indicates they will attend).

If the details of meetings change then a subsequent email (possibly a series of emails) are sent with the updated information. The email client will processed these automatically or semi-automatically, updating the calendar accordingly.

Describe the solution you'd like

I would like Indico to offer users the opportunity to "subscribe" (for what of a better word) to a category or meeting with their email address.

To protect against spam, such subscription requests would likely need to have some kind of protection, to verify that the owner of the email address was the person making the subscription request. For example, Indico could send an email (to verify the subscription) that contains a URL. The user would be invited to follow that URL, which would activate the corresponding subscription. (Care would also likely be needed to make sure these confirmation emails do not spam people.)

Once the subscription is confirmed, Indico would send emails to notify the user of the future events in the category. These emails would contain the details of these events using the standard format, allowing an email client to add the meeting details to some calendar (when the email client is so configured).

If the details of the meeting change (new meeting in the series, time of meeting changes, etc), then Indico would send update emails. These would be received by email clients, which would updated the information stored in the corresponding calendar.

Describe alternatives you've considered

The existing ics calendar export option provides an alternative possibility for synchronisation.

This is being investigated. It seems to works, but reportedly requires some additional steps (at least, for certain users) and (in any case) doesn't follow the group's existing approach.