Revert "MSC1730: Mechanism for redirecting to an alternative server during login"
Travis Ralston
6 years ago
committed by
GitHub
parent
a4bc79025b
commit
6dab287708
@ -1,152 +0,0 @@
|
||||
# MSC1730: Mechanism for redirecting to an alternative server during login
|
||||
|
||||
## Background/requirements
|
||||
|
||||
This is a proposal for a mechanism for handling the following situation.
|
||||
|
||||
A large, loosely-coupled organisation wants its members to be able to
|
||||
communicate with one another via Matrix. The organisation consists of several
|
||||
departments which are cooperative but prefer to host their own infrastructure.
|
||||
|
||||
The organisation has an existing single-sign-on system which covers the entire
|
||||
organisation, and which they would like their members to use when
|
||||
authenticating to the Matrix system.
|
||||
|
||||
## Proposal
|
||||
|
||||
The response to `POST /_matrix/client/r0/login` currently includes the fields
|
||||
`user_id`, `access_token`, `device_id`, and the deprecated `home_server`.
|
||||
|
||||
We will add to this the the field `well_known`, which has the same format as
|
||||
the [`/.well-known/matrix/client`
|
||||
object](https://matrix.org/docs/spec/client_server/r0.4.0.html#get-well-known-matrix-client).
|
||||
|
||||
Servers MAY add this field to the login response if they wish to redirect
|
||||
clients to an alternative homeserver after login. Clients SHOULD use the
|
||||
provided `well_known` object to reconfigure themselves, optionally validating the
|
||||
URLs within.
|
||||
|
||||
## Application
|
||||
|
||||
Let's imagine for this description that our organisation is the University of
|
||||
Canadialand, which is divided into departments including Engineering, History,
|
||||
Physics, and so on.
|
||||
|
||||
Central University IT currently host a SAML2-based single-sign-on system, which
|
||||
asks users to select their department, and then defers to the departmental
|
||||
authentication system to authenticate them. Note that the users do not have a
|
||||
globally-unique identifier.
|
||||
|
||||
University IT now sets up a Matrix Homeserver instance, which they host at
|
||||
`https://matrix.ac.cdl`. They run a publicity campaign encouraging university
|
||||
members to use the service by configuring off-the-shelf Matrix clients to use
|
||||
the homeserver at `https://matrix.ac.cdl`. They may also release customised
|
||||
clients configured to use that URL by default.
|
||||
|
||||
However, the departments actually want to host their own homeservers; these
|
||||
might be at `https://matrix.eng.ac.cdl`, `https://matrix.hist.ac.cdl`, etc. The
|
||||
central IT homeserver therefore redirects clients to the departmental
|
||||
homeserver after login.
|
||||
|
||||
A complete login flow is as shown in the following sequence diagram:
|
||||
|
||||
|
||||
|
||||
Note that this flow is complicated by the out-of-band SAML2 authentication. We
|
||||
envisage that a similar technique could also be used for a standard
|
||||
username/password authentication, however.
|
||||
|
||||
## Rejected solutions
|
||||
|
||||
Alternative solutions might include:
|
||||
|
||||
### Have all users on one homeserver
|
||||
|
||||
In many situtations, it might be more appropriate to have a single homeserver,
|
||||
so users' MXids would look like `@user:ac.cdl` instead of
|
||||
`@user:eng.ac.cdl`.
|
||||
|
||||
However, there are circumstances where separate homeservers are required:
|
||||
|
||||
* the departments may be only very loosely related
|
||||
* the departments may have privacy concerns
|
||||
* the dpeartments may be geographically distributed with slow or unreliable
|
||||
links to the central system
|
||||
* load-balancing may be essential.
|
||||
|
||||
### Tell users the C-S API for their home homeserver
|
||||
|
||||
We could tell Engineering users to configure their clients with
|
||||
`https://matrix.eng.ac.cdl`, History users to use `https://matrix.hist.ac.cdl`,
|
||||
etc.
|
||||
|
||||
The problems with this are:
|
||||
|
||||
* Each department must issue its own documentation and publicity advising how
|
||||
to configure a Matrix client
|
||||
|
||||
* It becomes impractical to distribute preconfigured clients.
|
||||
|
||||
### Proxy all C-S endpoints
|
||||
|
||||
It would be possible for the the central homeserver to proxy all C-S
|
||||
interaction, as well as `/login`, directing requests to the right server for
|
||||
the user.
|
||||
|
||||
This is unsatisfactory due to the additional latency imposed, the load on the
|
||||
central homeserver, and the fact that it makes the central server a single
|
||||
point of failure for the entire system.
|
||||
|
||||
### Require clients to perform a .well-known lookup after login
|
||||
|
||||
We could require clients to do a .well-known lookup on the domain of their MXID
|
||||
once they have discovered it from the `/login` response.
|
||||
|
||||
This has the following problems:
|
||||
|
||||
* In most cases this `.well-known` lookup will be entirely redundant. It adds
|
||||
latency and overhead, and complicates client implementations.
|
||||
|
||||
* It complicates deployment, since each department has to host a `.well-known`
|
||||
file at their root domain.
|
||||
|
||||
### Add an alternative redirection mechanism in the login flow
|
||||
|
||||
We could specify that the `/login` response could contain a `redirect` field
|
||||
property instead of the existing `user_id`/`access_token`/`device_id`
|
||||
properties. The `redirect` property would give the C-S API of the target
|
||||
HS. The client would then repeat its `/login` request, and use the specified
|
||||
endpoint for all future C-S interaction.
|
||||
|
||||
This approach would complicate client implementations.
|
||||
|
||||
### Modify the single-sign-on flow
|
||||
|
||||
It would be possible to modify the single-sign-on flow to allow an alternative
|
||||
homeserver to be specified for the final `m.login.token`-based call to
|
||||
`/login` (and subsequent C-S API calls).
|
||||
|
||||
This is discussed in more detail in
|
||||
[MSC1731](https://github.com/matrix-org/matrix-doc/blob/rav/proposals/homeserver_in_sso_login/proposals/1731-redirect-in-sso-login.md).
|
||||
|
||||
It has the disadvantage of limiting the solution to SSO logins. The solution
|
||||
presented in this proposal also extends to password-based logins.
|
||||
|
||||
### Use a 3pid login flow
|
||||
|
||||
It has been suggested that we could use a login flow based on third-party
|
||||
identifiers.
|
||||
|
||||
In the current ecosystem, to do a 3pid login, clients must still be configured
|
||||
to send their `/login` request to a particular homeserver, which will then take
|
||||
them through an authentication process. We are therefore still left with the
|
||||
problem that we need to switch homeservers between login and initial sync.
|
||||
|
||||
An alternative would be for clients to somehow know that they should go through
|
||||
the single-sign-on process *before* choosing a homeserver, and for the
|
||||
output of the single-sign-on process to indicate the homeserver to use. This
|
||||
would require either substantially customised Matrix clients, or substantial
|
||||
modifications to the login flow in Matrix, possibly involving authenticating
|
||||
against an identity server. The latter is something which could be considered,
|
||||
but the scope of the changes required make it impractical in the short/medium
|
||||
term.
|
||||
File diff suppressed because one or more lines are too long
|
Before Width: | Height: | Size: 35 KiB |
@ -1,43 +0,0 @@
|
||||
# https://sequencediagram.org/
|
||||
|
||||
participantspacing equal
|
||||
participant Client
|
||||
participant matrix.ac.cdl
|
||||
participant SAML2 SSO system
|
||||
participant matrix.eng.ac.cdl
|
||||
|
||||
activate Client
|
||||
|
||||
Client->matrix.ac.cdl:""GET /_matrix/client/r0/login""
|
||||
activate matrix.ac.cdl
|
||||
Client<--matrix.ac.cdl:"""type": "m.login.sso"""
|
||||
deactivate matrix.ac.cdl
|
||||
# Start SSO flow: displayed in browser for web clients, or via fallback auth in embeddedbrowser for others
|
||||
Client->matrix.ac.cdl:""GET /_matrix/client/r0/login/sso/redirect\n--?redirectUrl=<clienturl>--""
|
||||
activate matrix.ac.cdl
|
||||
matrix.ac.cdl->matrix.ac.cdl:Generate SAML request
|
||||
Client<--matrix.ac.cdl:302 to SSO system
|
||||
deactivate matrix.ac.cdl
|
||||
Client->SAML2 SSO system:""GET /single-sign-on\n--?SAMLRequest=<request>&RelayState=<clienturl>--""
|
||||
activate SAML2 SSO system
|
||||
Client<-->SAML2 SSO system: auth credentials
|
||||
SAML2 SSO system-->Client:auto-submitting HTML form including SAML Response
|
||||
deactivate SAML2 SSO system
|
||||
Client->matrix.ac.cdl:""POST /SAML2\n--SAMLResponse=<response>\nRelayState=<params>
|
||||
activate matrix.ac.cdl
|
||||
matrix.ac.cdl->matrix.ac.cdl:map user to HS
|
||||
Client<--matrix.ac.cdl:auto-submitting HTML form for target HS
|
||||
deactivate matrix.ac.cdl
|
||||
Client->matrix.eng.ac.cdl:""POST /SAML2\n--SAMLResponse=<response>\nRelayState=<clienturl>
|
||||
activate matrix.eng.ac.cdl
|
||||
Client<--matrix.eng.ac.cdl:302 to clienturl with\n""--?loginToken=<token>
|
||||
deactivate matrix.eng.ac.cdl
|
||||
Client->matrix.ac.cdl:""POST /_matrix/client/r0/login\n--{"type": "m.login.token","token": "<token>"}
|
||||
activate matrix.ac.cdl
|
||||
matrix.ac.cdl->matrix.eng.ac.cdl:""POST /_matrix/client/r0/login\n--{"type": "m.login.token", "token": "<token>"}
|
||||
activate matrix.eng.ac.cdl
|
||||
matrix.ac.cdl<--matrix.eng.ac.cdl:""--{"user_id": "@user:eng.ac.cdl", "access_token": "abc123",\n "well_known": {"m.homeserver": "..."}}
|
||||
deactivate matrix.eng.ac.cdl
|
||||
Client<--matrix.ac.cdl:""--{"user_id": "@user:eng.ac.cdl",\n "access_token": "abc123",\n "well-known": {"m.homeserver": "..."}}
|
||||
deactivate matrix.ac.cdl
|
||||
Client<-#0000FF>matrix.eng.ac.cdl: Matrix
|
||||
Loading…
Reference in New Issue