Identity Service API

The Matrix client-server and server-server APIs are largely expressed in Matrix user identifiers. From time to time, it is useful to refer to users by other ("third-party") identifiers, or "3pid"s, e.g. their email address or phone number. This identity service specification describes how mappings between third-party identifiers and Matrix user identifiers can be established, validated, and used. This description technically may apply to any 3pid, but in practice has only been applied specifically to email addresses.

1   Specification version

This version of the specification is generated from matrix-doc as of Git commit master,6a048ac.

2   General principles

The purpose of an identity service is to validate, store, and answer questions about the identities of users. In particular, it stores associations of the form "identifier X represents the same user as identifier Y", where identities may exist on different systems (such as email addresses, phone numbers, Matrix user IDs, etc).

The identity service has some private-public keypairs. When asked about an association, it will sign details of the association with its private key. Clients may validate the assertions about associations by verifying the signature with the public key of the identity service.

In general, identity services are treated as reliable oracles. They do not necessarily provide evidence that they have validated associations, but claim to have done so. Establishing the trustworthiness of an individual identity service is left as an exercise for the client.

3   Privacy

Identity is a privacy-sensitive issue. While the identity service exists to provide identity information, access should be restricted to avoid leaking potentially sensitive data. In particular, being able to construct large-scale connections between identities should be avoided. To this end, in general APIs should allow a 3pid to be mapped to a Matrix user identity, but not in the other direction (i.e. one should not be able to get all 3pids associated with a Matrix user ID, or get all 3pids associated with a 3pid).

4   Key management

An identity service has some long-term public-private keypairs. These are named in a scheme algorithm:identifier, e.g. ed25519:0. When signing an association, the Matrix standard JSON signing format is used, as specified in the server-server API specification under the heading "Signing Events".

In the event of key compromise, the identity service may revoke any of its keys. An HTTP API is offered to get public keys, and check whether a particular key is valid.

The identity server may also keep track of some short-term public-private keypairs, which may have different usage and lifetime characteristics than the service's long-term keys.

4.1   GET /_matrix/identity/api/v1/pubkey/{keyId}

Get the public key for the passed key ID.

Request format:

Parameter Type Description
path parameters
keyId string Required. The ID of the key. This should take the form algorithm:identifier where algorithm identifies the signing algorithm, and the identifier is an opaque string.

Response format:

Parameter Type Description
public_key string  

Example request:

GET /_matrix/identity/api/v1/pubkey/ed25519%3A0 HTTP/1.1

Response:

Status code 200:

The public key exists.

Example

{
  "public_key": "VXuGitF39UH5iRfvbIknlvlAVKgD1BsLDMvBf0pmp7c"
}

4.2   GET /_matrix/identity/api/v1/pubkey/isvalid

Check whether a long-term public key is valid.

Request format:

Parameter Type Description
query parameters
public_key string Required. The unpadded base64-encoded public key to check.

Response format:

Parameter Type Description
valid boolean Whether the public key is recognised and is currently valid.

Example request:

GET /_matrix/identity/api/v1/pubkey/isvalid?public_key=VXuGitF39UH5iRfvbIknlvlAVKgD1BsLDMvBf0pmp7c HTTP/1.1

Response:

Status code 200:

The validity of the public key.

Example

{
  "valid": true
}

4.3   GET /_matrix/identity/api/v1/pubkey/ephemeral/isvalid

Check whether a short-term public key is valid.

Request format:

Parameter Type Description
query parameters
public_key string Required. The unpadded base64-encoded public key to check.

Response format:

Parameter Type Description
valid boolean Whether the public key is recognised and is currently valid.

Example request:

GET /_matrix/identity/api/v1/pubkey/ephemeral/isvalid?public_key=VXuGitF39UH5iRfvbIknlvlAVKgD1BsLDMvBf0pmp7c HTTP/1.1

Response:

Status code 200:

The validity of the public key.

Example

{
  "valid": true
}

5   Association Lookup

5.1   GET /_matrix/identity/api/v1/lookup

Look up the Matrix user ID for a 3pid.

Request format:

Parameter Type Description
query parameters
medium string Required. The literal string "email".
address string Required. The email address being looked up.

Response format:

Parameter Type Description
address string The 3pid address of the user being looked up.
medium string The literal string "email".
mxid string The Matrix user ID associated with the 3pid.
not_before integer A unix timestamp before which the association is not known to be valid.
not_after integer A unix timestamp after which the association is not known to be valid.
ts integer The unix timestamp at which the association was verified.
signatures object The signatures of the verifying identity service which show that the association should be trusted, if you trust the verifying identity service.

Example request:

GET /_matrix/identity/api/v1/lookup?medium=email&address=louise%40bobs.burgers HTTP/1.1

Response:

Status code 200:

The association for that 3pid, or the empty object if no association is known.

Example

{
  "address": "louise@bobs.burgers",
  "medium": "email",
  "mxid": "@ears:matrix.org",
  "not_before": 1428825849161,
  "not_after": 4582425849161,
  "ts": 1428825849161,

  "signatures": {
    "matrix.org": {
      "ed25519:0": "ENiU2YORYUJgE6WBMitU0mppbQjidDLanAusj8XS2nVRHPu+0t42OKA/r6zV6i2MzUbNQ3c3MiLScJuSsOiVDQ"
    }
  }
}

6   Establishing Associations

The flow for creating an association is session-based.

Within a session, one may prove that one has ownership of a 3pid. Once this has been established, the user can form an association between that 3pid and a Matrix user ID. Note that this association is only proved one way; a user can associate any Matrix user ID with a validated 3pid, i.e. I can claim that any email address I own is associated with @billg:microsoft.com.

Sessions are time-limited; a session is considered to have been modified when it was created, and then when a validation is performed within it. A session can only be checked for validation, and validation can only be performed within a session, within a 24 hour period since its most recent modification. Any attempts to perform these actions after the expiry will be rejected, and a new session should be created and used instead.

6.1   Creating a session

A client makes a call to:

POST https://my.id.server:8090/_matrix/identity/api/v1/validate/email/requestToken

client_secret=monkeys_are_GREAT&
email=foo@bar.com&
send_attempt=1

It may also optionally specify next_link. If next_link is specified, when the validation is completed, the identity service will redirect the user to that URL.

This will create a new "session" on the identity service, identified by an sid.

The identity service will send an email containing a token. If that token is presented to the identity service in the future, it indicates that that user was able to read the email for that email address, and so we validate ownership of the email address.

We return the sid generated for this session to the caller, in a JSON object containing the sid key.

If a send_attempt is specified, the server will only send an email if the send_attempt is a number greater than the most recent one which it has seen (or if it has never seen one), scoped to that email address + client_secret pair. This is to avoid repeatedly sending the same email in the case of request retries between the POSTing user and the identity service. The client should increment this value if they desire a new email (e.g. a reminder) to be sent.

Note that Home Servers offer APIs that proxy this API, adding additional behaviour on top, for example, /register/email/requestToken is designed specifically for use when registering an account and therefore will inform the user if the email address given is already registered on the server.

6.2   Validating ownership of an email

A user may make either a GET or a POST request to /_matrix/identity/api/v1/validate/email/submitToken with the following parameters (either as query parameters or URL-encoded POST parameters): - sid the sid for the session, generated by the requestToken call. - client_secret the client secret which was supplied to the requestToken call. - token the token generated by the requestToken call, and emailed to the user.

If these three values are consistent with a set generated by a requestToken call, ownership of the email address is considered to have been validated. This does not publish any information publicly, or associate the email address with any Matrix user ID. Specifically, calls to /lookup will not show a binding.

Otherwise, an error will be returned.

6.3   Checking non-published 3pid ownership

A client can check whether ownership of a 3pid was validated by making an HTTP GET request to /_matrix/identity/api/v1/3pid/getValidated3pid, passing the sid and client_secret as query parameters from the requestToken call.

It will return something of either the form:

{"medium": "email", "validated_at": 1457622739026, "address": "foo@bar.com"}

or:

{"errcode": "M_SESSION_NOT_VALIDATED", "error": "This validation session has not yet been completed"}

If the sid and client_secret were not recognised, or were not correct, an error will be returned.

6.4   Publishing a validated association

An association between a session and a Matrix user ID can be published by making a URL-encoded HTTP POST request to /_matrix/identity/api/v1/3pid/bind with the following parameters:

sid=sid&
client_secret=monkeys_are_GREAT&
mxid=@foo:bar.com

If the session is still valid, this will publish an association between the 3pids validated on that session and the passed Matrix user ID. Future calls to /lookup for any of the session's 3pids will return this association.

If the 3pid has not yet been validated, the HTTP request will be rejected, and the association will not be established.

If the sid and client_secret were not recognised, or were not correct, an error will be returned.

7   Invitation Storage

An identity service can store pending invitations to a user's 3pid, which will be retrieved and can be either notified on or look up when the 3pid is associated with a Matrix user ID.

If one makes a POST request to /_matrix/identity/api/v1/store-invite with the following URL-encoded POST parameters:

  • medium (string, required): The literal string email.
  • address (string, required): The email address of the invited user.
  • room_id (string, required): The Matrix room ID to which the user is invited.
  • sender (string, required): The matrix user ID of the inviting user.

An arbitrary number of other parameters may also be specified. These may be used in the email generation described below.

The service will look up whether the 3pid is bound to a Matrix user ID. If it is, the request will be rejected with a 400 status code.

If the medium is something other than the literal string email, the request will be rejected with a 400 status code.

Otherwise, the service will then generate a random string called token, and an ephemeral public key.

The service also generates a display_name for the inviter, which is a redacted version of address which does not leak the full contents of the address.

The service records persistently all of the above information.

It also generates an email containing all of this data, sent to the address parameter, notifying them of the invitation.

The response body is then populated as the JSON-encoded dictionary containing the following fields: - token (string): The generated token. - public_keys ([string]): A list of [server's long-term public key, generated ephemeral public key]. - display_name (string): The generated (redacted) display_name.

At a later point, if the owner of that particular 3pid binds it with a Matrix user ID, the identity server will attempt to make an HTTP POST to the Matrix user's homeserver which looks roughly as below:

POST https://bar.com:8448/_matrix/federation/v1/3pid/onbind
Content-Type: application/json

{
  "invites": [{
    "mxid": "@foo:bar.com",
    "token": "abc123",
    "signatures": {
      "my.id.server": {
        "ed25519:0": "def987"
      }
    }
  }],

  "medium": "email",
  "address": "foo@bar.com",
  "mxid": "@foo:bar.com"
}

Where the signature is produced using a long-term private key.

Also, the generated ephemeral public key will be listed as valid on requests to /_matrix/identity/api/v1/pubkey/ephemeral/isvalid.

8   Ephemeral invitation signing

To aid clients who may not be able to perform crypto themselves, the identity service offers some crypto functionality to help in accepting invitations. This is less secure than the client doing it itself, but may be useful where this isn't possible.

The identity service will happily sign invitation details with a request-specified ed25519 private key for you, if you want it to. It takes URL-encoded POST parameters: - mxid (string, required) - token (string, required) - private_key (string, required): The private key, encoded as Unpadded base64.

It will look up token which was stored in a call to store-invite, and fetch the sender of the invite. It will then respond with JSON which looks something like:

{
  "mxid": "@foo:bar.com",
  "sender": "@baz:bar.com",
  "signatures" {
    "my.id.server": {
      "ed25519:0": "def987"
    }
  },
  "token": "abc123"
}