initial proposal

pull/977/head
Will Hunt 4 years ago
parent 89a3663372
commit 61a8866683

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# MSC0000: Provide authentication method for appservice users
Appservices within Matrix are increasingly attempting to support End-to-End Encryption. As such, they
need a way to generate devices for their users so that they can participate in E2E rooms. In order to
do so, this proposal suggests implementing an appservice extension to the
[`POST /login` endpoint](https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-login).
Appservice users do not usually need to login as they do not need their own access token, and do not
traditionally need a "device". However E2E encryption demands that all users in a room have a device
which means bridge users need to be able to generate a device on demand.
## Proposal
A new `type` is to be added to `POST /login`.
`m.login.application_service`
The `/login` endpoint may now take an `access_token` in the same way that other
authenticated endpoints do. No additional parameters should be specified in the request body.
Example request
```json
{
"type": "m.login.application_service",
"identifier": {
"type": "m.id.user",
"user": "alice"
}
}
```
The response body should be unchanged from the existing `/login` specification.
If
- The access token is not provided
- The access token does not correspond to a appservice
- The access token does not correspond to a appservice that manages this user
- Or the user has not previously been registered
Then the servers should reject with HTTP 403, with an `errcode` of `"M_FORBIDDEN"`.
Homeservers should ignore the `access_token` parameter if a type other than
`m.login.application_service` has been provided.
The expected flow for appservices would be to `/register` their users, and
then `/login` to generate the appropraite device.
## Potential issues
This proposal means that there will be more calls to make when setting up a appservice user, when
using encryption. While this could be done during the registration step, this would prohibit creating
new devices should the appservice intentionally or inadvertently lost the client-side device data.
## Alternatives
One minor tweak to the current proposal could be to include the token as part of the auth data, rather than
being part of the header/params to the request. An argument could be made for either, but since the specification
expects the appservice to pass the token this way in all requests, including /register it seems wise to keep
it that way.
Some community members have used implementation details such as a "shared secret" authentication method to
log into the accounts without having to use the /login process at all. Synapse provides such a function,
but also means the appservice can now authenticate as any user on the homeserver.
A third option could be to create a new endpoint that simply creates a new device for an appservice user on demand.
Given the rest of the matrix eco-system does this with /login, and /login is already extensible with `type`, it would
create more work for all parties involved for little benefit.
## Security considerations
The /login endpoint will generate an access token which can be used to control the appservice user, which
is superflous as the appservice `as_token` should be used to authenticate all requests on behalf of ghosts.
This can safely be ignored or used, but is an extra token hanging around.
## Unstable prefix
Implementations should use `uk.half-shot.mscXXXX.login.application_service` for `type` given in the
`POST /login` until this lands in a released version of the specification.
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