MSC2461: Proposal for Authenticated Content Repository API #2461

SyrupThinker · 2020-03-15T04:00:30Z

Signed-off-by: Valentin Anger <syrupthinker@gryphno.de>

Sorunome

Nice idea, a few things aren't clear to soru, though

Sorunome · 2020-03-15T08:20:37Z

proposals/2461-authenticated-content-repository-api.md

+| ---------- | ----------- |
+| null / missing | All content can be accessed unauthenticated |
+| m.cached | Only cached content can be accessed unauthenticated |
+| m.local | Only content with an authority the server is responsible for can be accessed unauthenticated |


What does this mean? Basically all users in the room can see it, but noone else?

See other comment.
Does the new context clarify the meaning of this?
Because to me it is phrased very clearly.

Sorunome · 2020-03-15T08:21:06Z

proposals/2461-authenticated-content-repository-api.md

+| Enum value | Description |
+| ---------- | ----------- |
+| null / missing | All content can be accessed unauthenticated |
+| m.cached | Only cached content can be accessed unauthenticated |


Is this even needed? It sounds odd - someone in the room accesses the content and then suddenly everyone can as it is cached

Replying to the first part of the question, as the latter is unrelated as clarified elsewhere.
This is based on Mathew's comment in synapse#2133.
One possible use case for m.cached is that a server admin knows that all users are responsible and allows content that they accessed (and then for exampled didn't report) to be accessed by older clients and to be directly linked to for bridges or download links.

Sorunome · 2020-03-15T08:21:41Z

proposals/2461-authenticated-content-repository-api.md

+
+### Configuration
+To allow clients to predetermine whether authentication is required,
+the configuration field m.media.unauthenticated is added.


Added where? To which endpoint? Down there you have that as a reply and not as sending, so something is off

Added endpoint in new revision

Sorunome · 2020-03-15T08:22:25Z

proposals/2461-authenticated-content-repository-api.md

+}
+```
+
+Clients can decide based on this


why not add the authentification type to m.file etc.? So like

{ "url": "blah", "info": { ... }, "authenticated": "m.local" }

I might have miscommunicated the intent of this proposal by adding synapse#2150 considering it is only tagentally related. I've read the conversation some time ago and added it from memory. Only checking whether I cought the issues I was thinking of.

I have clarified the intent in a new revision.

Signed-off-by: Valentin Anger <syrupthinker@gryphno.de>

SyrupThinker · 2020-03-21T12:31:26Z

proposals/2461-authenticated-content-repository-api.md

+`GET /_matrix/media/r0/config`.
+It specifies what content can be accessed unauthenticated.
+
+The following behaviours are defined:


Threaded discussions are preferred @helaan

m.local Correct, it also allows compliance with local regulations regarding the possession and distribution of illegal content.

m.cached Not quite, if the server already fetched the content (or it originated on this server), unauthenticated users can access it. Maybe m.stored is less confusing?

m.none and null / missing Exactly.

m.unspecified The server could use different criteria to allow access to content, that are not covered by this document.
This is basically the fallback case of "you need to check to know whether you can access something".
One might also call it arbitrary, but I didn't want the connotation of
it never being consistent.

An unpublished version contained "Each entry in the following table is a subset of the preceding ones, with m.unspecified not fitting into this hierarchy".

Ah, I'll switch to threaded replies then.

An unpublished version contained "Each entry in the following table is a subset of the preceding ones, with m.unspecified not fitting into this hierarchy".
That makes it a lot clearer, I did not pick up on m.cached being comparable to m.local.

About m.none: Maybe state more clearly that this is only possible on unfederated servers?

What do you think will be the mode that servers in the public federation will use when this MSC is implemented and it is worth it to have it flexible? Personally, I think federated servers will switch to m.local and unfederated servers will just use m.none. Wouldn't this be simpler and as effective to have this setting depend on whether or not you have federation enabled or am I underestimating the importance of old client support?

In my opinion m.none is not just possible on unfederated servers. Having m.none as the default for unfederated servers seems sensible, but concluding that when a server federates it will always have an accessible content repo is wrong. An admin might just not want to distribute through the media endpoints regardless.

I agree m.local would be the most common case for federated servers.

Especially m.cached gives nice properties like explained in the MSC. Although that could be cut and signaled through m.unspecified, loosing the benefit of clients knowing they can link to the content directly.

Having m.unspecified forces client and server authors to think about the possibility of rejection, something that some current clients don't do. It empowers admins to have a different rule set without clients failing when they make assumptions for the other cases.
Maybe this should be replaced or amended with "When an unknown value is encountered a client should account for the possibility of rejection".

Preserving compatibility with older clients is also a choice admins should make.
Explicitly supporting the old behavior allows this.

If I were to create the simplest form of this proposal it would just state.

All unauthenticated accesses to media endpoints may be rejected for any reason

turt2live

Generally is a good idea, but the footgun on exploiting your own account will need solving.

turt2live · 2020-03-27T01:12:28Z

proposals/2461-authenticated-content-repository-api.md

+Additionally older clients and servers might encounter an unexpected error code
+which may lead to unknown behaviour.
+
+## Alternatives


This will need a section comparing it to MSC701

turt2live · 2020-03-27T01:13:22Z

proposals/2461-authenticated-content-repository-api.md

+
+### Configuration
+To allow clients to predetermine whether authentication is required,
+the field m.media.unauthenticated is added to


generally we should be naming things in the positive:

Suggested change

the field m.media.unauthenticated is added to

the field m.media.authenticated is added to

This would lead to the inverted enum values m.non-local and m.uncached
which are in my opinion worse than having the field name in the negative.

I'm open to suggestions for better enum names

tbh when I was leaving this comment I was expecting it to be a boolean, not an enum. Not sure there's a benefit for having it be an enum at all, or even really needing this flag is needed.

Well, that depends on whether servers can actually make use of that value (according to you they should not) and whether its considered useful enough for clients (as noted in the MSC).

If those are not considered useful then all that stuff can be thrown out.

turt2live · 2020-03-27T01:14:46Z

proposals/2461-authenticated-content-repository-api.md

+### Server to server
+To reduce the amount of server to server communication,
+when one homeserver tries to fetch content from another homeserver,
+the configuration should first be retrieved and cached.


There is no federation API for this.

I figured that because servers use the client API for media downloads they could also use it for the media config endpoint

They cannot. Also they aren't supposed to be using the client endpoints, they just haven't been defined correctly in the server-side endpoints.

Then this proposal is the time to specify that I'd say. Sharing media will be hard.

Maybe the "federation api" could be an extra query parameter on existing download/thumbnail endpoints, which can be as simple as authed=yes/no? Of course, servers would need to also authenticate that it is another server that is requesting such media, and not someone else.

turt2live · 2020-03-27T01:15:55Z

proposals/2461-authenticated-content-repository-api.md

+
+## Potential issues
+Once homeservers enable this behaviour with a m.media.unauthenticated
+value other than null, older clients will not be able to access some content.


Not only older clients, but many desktop clients will have a hard time accessing images now. Some of the toolkits people use don't allow them to add headers before the request, so they'd need to add special code for this to buffer the media ahead of time.

This isn't a problem we need to fix in the MSC though, just something to be aware of.

turt2live · 2020-03-27T01:17:31Z

proposals/2461-authenticated-content-repository-api.md

+`GET /_matrix/media/r0/config`.
+It specifies what content can be accessed unauthenticated.
+
+The following behaviours are defined:


I'd generally just recommend we have it turned on for the client-server API regardless. There's nothing stopping a server from accepting lack of auth, and realistically the spec should fix the general case of media being locked down.

Such a change should only happen after some server-server API is in place though, right?
Otherwise media couldn't be fetched from a strictly conforming server.

turt2live · 2020-03-27T01:18:42Z

proposals/2461-authenticated-content-repository-api.md

+}
+```
+
+## Potential issues


Also mentioned in MSC701 (I think, I'm going off memory) is a way to solve the authentication issue without potentially leaking your access token. Clients which have 'download this file' or 'open in new tab' buttons will need to pass along the access token via the query string. In doing so, when someone copies the link and pastes it to someone else they've exposed their account.

I really try to stay away from crypto, so this is just a naive simplification of MSC701:

The authentication token is created through HMAC(access_token, media_id).
This way only the media download can be replayed.
I'm not sure how the HMAC would be verified, but that'd need to be solved for MSC701 as well.

- Specify behaviour on unknown enum values - Include points brought up by turt2live - Draw a comparison to MSC701 - Formatting Signed-off-by: Valentin Anger <syrupthinker@gryphno.de>

ShadowJonathan

I like this idea, but I think it has a fatal flaw and confusion with m.none that i'd like to see resolved first.

ShadowJonathan · 2021-04-19T12:19:30Z

proposals/2461-authenticated-content-repository-api.md

+
+| Enum value     | Description                                                                                  |
+| ----------     | -----------                                                                                  |
+| null / missing | All content can be accessed unauthenticated                                                  |


I'm seeing m.none mentioned below, should that one be added here? Or what's the status on that?

null should actually be m.none here, thanks for pointing that out.

ShadowJonathan · 2021-04-19T12:20:52Z

proposals/2461-authenticated-content-repository-api.md

+To reduce the amount of server to server communication,
+when one homeserver tries to fetch content from another homeserver,
+the configuration should first be retrieved and cached.
+When the value is m.none the server should not attempt to fetch the


Does m.none effectively mean "All content uploaded on here is non-accessible to other servers"? that breaks quite a lot of (core) assumptions in matrix, where f.e. someone setting a room avatar in a federated room can suddenly "not display" that avatar simply because the server does not allow federated propagation of that file, per server-wide rules.

I assume my other comment clears the first part up, but m.none actually means no restrictions, as in the current behaviour. m.all would actually be the behaviour you describe, as in everything is restricted.

For the latter, yes, that is an expected consequence of this proposal.
I'd expect a user to be made aware by server owners if such media restrictions are in place.

"restricted" as in "can only be accessed once authenticated"? And that any server over federation can request such media in an authenticated user's stead?

turt2live · 2024-04-23T03:12:25Z

@SyrupThinker Thanks for opening this MSC! We've been considering authentication for quite a while, and really appreciate efforts to fix this particular area of the protocol. Lately we've been working on #3916 as a way forward to authentication, and are currently gearing up for acceptance on it.

If there's something we haven't yet considered in MSC3916 that you think we should, let us know. It's our current proposal to close this MSC in favour of MSC3916.

Proposal for Authenticated Content Repository API

74dea68

Signed-off-by: Valentin Anger <syrupthinker@gryphno.de>

SyrupThinker changed the title ~~Proposal for Authenticated Content Repository API~~ MSC2461: Proposal for Authenticated Content Repository API Mar 15, 2020

turt2live added proposal A matrix spec change proposal proposal-in-review labels Mar 15, 2020

turt2live self-requested a review March 15, 2020 06:04

Sorunome reviewed Mar 15, 2020

View reviewed changes

Clarify intent in MSC2461

d10e27b

Signed-off-by: Valentin Anger <syrupthinker@gryphno.de>

This comment has been minimized.

Sign in to view

SyrupThinker commented Mar 21, 2020

View reviewed changes

turt2live requested changes Mar 27, 2020

View reviewed changes

MSC2461 Revision 3

c036c71

- Specify behaviour on unknown enum values - Include points brought up by turt2live - Draw a comparison to MSC701 - Formatting Signed-off-by: Valentin Anger <syrupthinker@gryphno.de>

turt2live added kind:feature MSC for not-core and not-maintenance stuff kind:maintenance MSC which clarifies/updates existing spec and removed kind:feature MSC for not-core and not-maintenance stuff labels Apr 20, 2020

auscompgeek mentioned this pull request Nov 13, 2020

MSC2858: Multiple SSO Identity Providers #2858

Merged

ShadowJonathan suggested changes Apr 19, 2021

View reviewed changes

MSC2461 Revision 4

c49b2f6

SyrupThinker requested a review from turt2live April 19, 2021 15:28

turt2live removed their request for review April 19, 2021 15:46

turt2live added the needs-implementation This MSC does not have a qualifying implementation for the SCT to review. The MSC cannot enter FCP. label Jun 8, 2021

turt2live force-pushed the old_master branch from e895827 to dca99ee Compare August 30, 2021 22:34

richvdh mentioned this pull request Dec 24, 2021

Auth for content repo (and enforcing GDPR erasure) #3796

Open

babolivier mentioned this pull request Dec 24, 2021

Media in the content repo is not authed matrix-org/matrix-spec#870

Open

turt2live removed the proposal-in-review label May 5, 2022

nephele-gh mentioned this pull request Oct 24, 2022

MSC3916: Authentication for media #3916

Open

	the field m.media.unauthenticated is added to
	the field m.media.authenticated is added to

MSC2461: Proposal for Authenticated Content Repository API #2461

Are you sure you want to change the base?

MSC2461: Proposal for Authenticated Content Repository API #2461

Conversation

SyrupThinker commented Mar 15, 2020

Sorunome left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

This comment has been minimized.

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

turt2live left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

SyrupThinker Mar 28, 2020 • edited

Choose a reason for hiding this comment

Choose a reason for hiding this comment

SyrupThinker Mar 28, 2020 • edited

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

SyrupThinker Mar 28, 2020 • edited

Choose a reason for hiding this comment

ShadowJonathan left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

ShadowJonathan Apr 19, 2021 • edited

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

turt2live commented Apr 23, 2024

SyrupThinker Mar 28, 2020 •

edited

SyrupThinker Mar 28, 2020 •

edited

SyrupThinker Mar 28, 2020 •

edited

ShadowJonathan Apr 19, 2021 •

edited