Make some keys immutable

[gkc]

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

Currently it is possible for an authenticated client to make problematic updates. Currently we try to avoid client software doing these problematic things; however we need a mechanism to prevent these updates occurring.

Here are some of the keys whose values should not be permitted to be overwritten

• public:publickey@alice
• privatekey:at_pkam_publickey
• shared_key.bob@alice

Describe the solution you'd like

For public:publickey@alice and privatekey:at_pkam_publickey we should prevent their value being modified by client updates (i.e. the update verb handler)

For shared_key.bob@alice we should also prevent the value being modified by client updates.

We should allow metadata to be updated. TBD whether there is some metadata which we should prevent being updated

Describe alternatives you've considered

As the concept of limiting updates to data after its initial creation may have broader applicability, we could introduce a new metadata field, 'immutable', which defaults to false

However we could also just start by putting guards around the three keys named above.

Additional context

No response

[gkc]

Marking for discussion at an architecture call before we move to implementation

[XavierChanth]

Thoughts:

With an immutable key (i.e. immutable=true in the metadata) it would be good to disable edits (i.e. put) but still allow deletion. In addition, require some sort of override/force flag to be set to true when deleting an immutable key.

[Zambrella]

Idea: Add a re-authentication step to potentially harmful actions (e.g. mutatating keys that shouldn't be mutated). This would at least likely stop a bug from doing something it shouldn't.

[gkc]

Picking this up in this sprint as it is required for atsign-foundation/noports#1780

Required PRs in at_libraries (at_commons), at_server (at_persistence_secondary_server, at_secondary_server), at_client_sdk (at_client) and at_protocol (protocol spec)

2SP because I've completed most of it this morning