MSC3231: Token authenticated registration (#3231)
* Proposal for token authenticated registration Signed-off-by: Callum Brown <callum@calcuode.com> * Hard-wrap lines Signed-off-by: Callum Brown <callum@calcuode.com> * Link to released version of spec Signed-off-by: Callum Brown <callum@calcuode.com> * Fix unstable prefix wording Signed-off-by: Callum Brown <callum@calcuode.com> * Tokens should only be invalidated after registration Signed-off-by: Callum Brown <callum@calcuode.com> * Change auth type to m.login.registration_token This is consistent with the other UIAA auth types, and does not suggest that other `m.login.*` types cannot be used for registration. Signed-off-by: Callum Brown <callum@calcuode.com> * Add proposal for checking the validity of a token Signed-off-by: Callum Brown <callum@calcuode.com> * Fix validity checking endpoint Signed-off-by: Callum Brown <callum@calcuode.com> * Limit allowed characters and length of token This allows tokens to be used easily in query parameters Signed-off-by: Callum Brown <callum@calcuode.com> * Give reason for limiting token length and chars Signed-off-by: Callum Brown <callum@calcuode.com> * Note all stages must be complete for registration Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com> * Fix mistake in MSC number Signed-off-by: Callum Brown <callum@calcuode.com> * Validity checking should be rate limited Signed-off-by: Callum Brown <callum@calcuode.com> * Change v1 to r0 Signed-off-by: Callum Brown <callum@calcuode.com> * Include `.` and `~` in allowed characters for registration tokens For consistency with the unreserved URL characters in RFC3986 https://www.ietf.org/rfc/rfc3986.html#section-2.3 Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com> Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>pull/3778/head
Callum Brown
3 years ago
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# MSC3231: Token Authenticated Registration
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Currently, homeserver administrators must choose between allowing anyone to
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register and completely disabling registrations. This is a problem for
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administrators who want to let certain people have an account on their server,
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but do not want to register the accounts manually (possibly because the
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initial password may not be changed by the user).
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There are some existing external solutions (see the **Alternatives** section),
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but these require additional effort from administrators and are disconnected
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from Matrix clients. It would be useful for administrators to have a convenient
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method of limiting registrations to certain people which requires minimal setup
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and is integrated with existing clients.
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## Proposal
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The [/\_matrix/client/r0/register](https://matrix.org/docs/spec/client_server/r0.6.1#post-matrix-client-r0-register)
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endpoint uses the [User-Interactive Authentication API](https://matrix.org/docs/spec/client_server/r0.6.1#user-interactive-authentication-api).
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A new authentication type `m.login.registration_token` will be defined which requires
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a `token` key to be present in the submitted `auth` dict. The token will be a
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string of no more than 64 characters, and contain only characters matched by the
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regex `[A-Za-z0-9._~-]`.
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This will avoid URL encoding issues with the validity checking endpoint, and
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prevent DoS attacks from extremely long tokens.
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For example, when a client attempts registration with no `auth` dict, a server
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may respond with:
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```
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HTTP/1.1 401 Unauthorized
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{
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"flows": [
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{
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"stages": [ "m.login.registration_token" ]
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}
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],
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"params": {},
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"session": "xxxxx"
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}
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```
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The client would then prompt the user to enter a token and send a new request
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with an `auth` dict:
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```
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POST /_matrix/client/r0/register
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{
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"auth": {
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"type": "m.login.registration_token",
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"token": "fBVFdqVE",
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"session": "xxxxx"
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}
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"device_id": "ABC",
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"initial_device_display_name": "Some Client",
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"password": "badpassword",
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"username": "bob"
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}
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```
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If the server verifies that `fBVFdqVE` is a valid token then the account is
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registered as normal assuming all other required auth stages have been completed, otherwise a `401` status is returned. Once registration of
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the user has completed, the server may alter the validity of the token.
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For example, the token may be completely invalidated, or its number of permitted
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uses reduced. Management of the tokens is left to the server implementation.
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Using the User-Interactive Authentication API means clients' existing
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registration logic will be unaffected, with a fallback available for clients
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without native support for the new authentication type.
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### Checking the validity of a token
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A Client may wish to present username and password inputs only after it has
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checked the token is valid.
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Clients would be able to check the validity of a token in advance of
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registration with a `GET` request to
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`/_matrix/client/r0/register/m.login.registration_token/validity`.
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This endpoint would take a required `token` query parameter, and validity would be
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indicated by the boolean `valid` key in the response.
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For example, a client would send:
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```
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GET /_matrix/client/r0/register/m.login.registration_token/validity?token=abcd
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```
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If `abcd` is a valid token, the server would respond with:
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```
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HTTP/1.1 200 OK
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{
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"valid": true
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}
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```
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This does not perform any actual authentication, and the validity of the token
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may change between the check and the User-Interactive Authentication.
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This endpoint should be rate limited in order to prevent dictionary attacks.
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## Potential issues
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The new authentication type would only apply to the
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`/_matrix/client/r0/register` endpoint. This should not cause problems, but it
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would be worth noting in any change to the specification.
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## Alternatives
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[matrix-registration](https://github.com/ZerataX/matrix-registration/) is an
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application which provides token management and a standalone web interface.
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It uses Synapse's admin API to do registrations.
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[Midnight](https://github.com/KombuchaPrivacy/midnight) sits in front of a
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homeserver and handles the `/_matrix/client/r0/register` endpoint. It provides
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token management and does additional checks on the requested username.
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Registration requests are forwarded to the homeserver once authenticated.
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It uses the User-Interactive Authentication API in a very similar way to this
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MSC, which could allow existing Matrix clients to be used.
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[matrix-register-bot](https://github.com/krombel/matrix-register-bot) is a
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Matrix bot which allows registrations done through the provided web interface
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to be accepted or denied by users in a certain room. When a registration is
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approved temporary credentials are sent to the user's verified email address.
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It can use Synapse's admin API or [matrix-synapse-rest-auth](https://github.com/kamax-matrix/matrix-synapse-rest-password-provider#integrate)
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to do the registration.
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## Unstable prefix
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Implementations should use `org.matrix.msc3231.login.registration_token` as the
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authentication type until this MSC has passed FCP and been merged.
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Similarly, `/_matrix/client/unstable/org.matrix.msc3231/register/org.matrix.msc3231.login.registration_token/validity`
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should be used as the endpoint for checking the validity of a token in advance.
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