Authentication client-to-server

[jg10-mastodon-social]

As a user, I don't want to need a different login for each app.

This is often cited as a motivation for combining Solid and ActivityPub.

From a technical perspective the login is needed to:

1. identify which actor is being used
2. gain access to the ability to sign activities using the private key Public/private keypair #8 for sending Sending activities #14 and following Following activities #15 activities
3. gain read access to inbox and write access to outbox Actors' inbox and outbox #7

[jg10-mastodon-social]

At a basic level, if a webid is used for authentication, then this already provides a shared login across apps even if they use different actors.

A user may also want to be able to have multiple apps send activities as the same actor.
It seems that implementing an outbox is preferable to having multiple apps access the same private key. #14 (comment)

[jg10-mastodon-social]

Different from #20 , which mainly applies to server-to-server auth of messages.