Proposal for integration manager discovery

proposals/0000-integrations-discovery.md

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+# MSC0000: Integration manager discovery
+
+*Note*: This is a required component of [MSC1956 - Integrations API](https://github.com/matrix-org/matrix-doc/pull/1956)
+
+Users should have the freedom to choose which integration manager they want to use in their client, while
+also accepting suggestions from their homeserver and client. Clients need to know where to find the different
+integration managers and how to contact them.
+
+
+## Proposal
+
+A single logged in user may be influenced by zero or more integration managers at any given time. Managers
+are sourced from the client's own configuration, homeserver discovery information, and the user's personal
+account data in the form of widgets. Clients should support users using more than one integration manager
+at a given time, although the rules for how this can be handled are defined later in this proposal.
+
+#### Client-configured integration managers
+
+This is left as an implementation detail. In the case of Riot, this is likely to be part of the existing
+`config.json` options, although liekly modified to support multiple managers instead of one.
+
+#### Homeserver-configured integration managers
+
+The integration managers suggested by a homeserver are done through the existing
+[.well-known](https://matrix.org/docs/spec/client_server/r0.4.0.html#get-well-known-matrix-client) discovery
+mechanism. The added optional fields, which should not affect a client's ability to log a user in, are:
+```json
+{
+    "m.integrations": {
+        "managers": [
+            {
+                "api_url": "https://integrations.example.org",
+                "ui_url": "https://integrations.example.org/ui"
+            },
+            {
+                "api_url": "https://bots.example.org"
+            }
+        ]
+    }
+}
+```
+
+As shown, the homeserver is able to suggest multiple integration managers through this method. Each manager
+must have an `api_url` which must be an `http` or `https` URL. The `ui_url` is optional and if not provided
+is the same as the `api_url`. Like the `api_url`, the `ui_url` must be `http` or `https` if supplied.
+
+The `ui_url` is ultimately treated the same as a widget, except that the custom `data` is not present and
+must not be templated here. Variables like `$matrix_display_name` are able to function, however. Integration
+managers should never use the `$matrix_user_id` as authoritative and instead seek other ways to determine the
+user ID. This is covered by other proposals.
+
+The `api_url` is the URL clients will use when *not* embedding the integration manager, and instead showing
+its own purpose-built interface.
+
+#### User-configured integration managers
+
+Users can specify integration managers in the form of account widgets. The `type` is to be `m.integration_manager`
+and the content would look something similar to:
+```json
+{
+    "url": "https://integrations.example.org/ui?displayName=$matrix_display_name",
+    "data": {
+        "api_url": "https://integrations.example.org"
+    }
+}
+```
+
+The `api_url` in the `data` object is required and has the same meaning as the homeserver-defined `api_url`.
+The `url` of the widget is analogous to the `ui_url` from the homeserver configuration above, however normal
+widget rules apply here.
+
+The user is able to have multiple integration managers through use of multiple widgets.
+
+#### Display order of integration managers
+
+Clients which have support for integration managers should display at least 1 manager, but may decide
+to display multiple via something like tabs. Clients must prefer to display the user's configured
+integration managers over any defaults, and if only displaying one manager must pick the first
+manager after sorting the `state_key`s in lexicographical order. Clients may additionally display
+default managers if they so wish, and should preserve the order defined in the various defaults.
+If the user has no configured integration managers, the client must prefer to display one or more
+of the managers suggested by the homeserver over the managers recommended by the client.
+
+The client may optionally support a way to entirely disable integration manager support, even if the
+user and homeserver have managers defined.
+
+The rationale for having the client prefer to use the user's integration managers first is so that
+the user can tailor their experience within Matrix if desired. Similarly, a homeserver may wish to
+subject all of their users to the same common integration manager as would be common in some organizations.
+The client's own preference is a last ditch effort to have an integration manager available to the
+user so they don't get left out.
+
+#### Displaying integration managers
+
+Clients simply open the `ui_url` (or equivalent) in an `iframe` or similar. In the current ecosystem,
+integration managers would receive a `scalar_token` to idenitify the user - this is no longer the case
+and instead integration managers must seek other avenues for determining the user ID. Other proposals
+cover how to do this in the context of the integrations API.
+
+Integration managers shown in this way must be treated like widgets, regardless of source. In practice
+this means exposing the Widget API to the manager and applying necessary scoping to keep the manager
+as an account widget rather than a room widget.
+
+
+## Tradeoffs
+
+We could limit the user (and by extension, the homeserver and client) to exactly 1 integration manager
+and not worry about tabs or other concepts, however this restricts a user's access to integrations.
+In a scenario where the user wants to use widgets from Service A and bots from Service B, they'd
+end up switching accounts or clients to gain access to either service, or potentially just give up
+and walk away from the problem. Instead of having the user switch between clients, we might as well
+support this use case, even if it is moderately rare.
+
+We could also define the integration managers in a custom account data event rather than defining them
+as a widget. Doing so just adds clutter to the account data and risks duplicating code in clients as
+using widgets gets us URL templating for free (see the section later on in this proposal about account
+widgets for more information).
+
+
+## Future extensions
+
+Some things which may be desirable in the future are:
+* Avatars for the different managers
+* Human-readable names for the different managers
+* Supporting `ui_url`s targeting specific clients for a more consistent design
+
+
+## Security considerations
+
+When displaying integration managers, clients should not trust that the input is sanitary. Integration
+managers may only be at HTTP(S) endpoints and may still have malicious intent. Ensure any sandboxing
+on the manager is appropriate such that it can communicate with the client, but cannot perform unauthorized
+actions.