Merge e9526c7564 into 979264e923

Currently, the example for `ExportedSessionData` is missing values for
`room_id` and `session_id`.

Move the example field values for `KeyBackupSessionData` into the field
definitions, so that an example for the object as a whole is built
automatically, and when we extend it to form `ExportedSessionData` the
explicit example does not override the more complete autogenerated one.

changelogs/client_server/newsfragments/2147.new

@@ -0,0 +1 @@
+Add `GET /_matrix/client/v1/auth_metadata`, as per [MSC2965](https://github.com/matrix-org/matrix-spec-proposals/pull/2965).

changelogs/client_server/newsfragments/2149.feature

@@ -0,0 +1 @@
+Add the OAuth 2.0 based authentication API, as per [MSC3861](https://github.com/matrix-org/matrix-spec-proposals/pull/3861) and its sub-proposals.

changelogs/client_server/newsfragments/2150.feature

@@ -0,0 +1 @@
+Add the OAuth 2.0 based authentication API, as per [MSC3861](https://github.com/matrix-org/matrix-spec-proposals/pull/3861) and its sub-proposals.

changelogs/client_server/newsfragments/2154.clarification

@@ -0,0 +1 @@
+Add missing fields in example for `ExportedSessionData`.

content/client-server-api/_index.md

@@ -1481,6 +1481,345 @@ MAY reject weak passwords with an error code `M_WEAK_PASSWORD`.
 
 ### OAuth 2.0 API
 
+#### Server metadata discovery
+
+{{% http-api spec="client-server" api="oauth_server_metadata" %}}
+
+#### Scope
+
+The client requests a scope in the OAuth 2.0 authorization flow, which is then
+associated to the generated access and refresh tokens. This provides a framework
+for obtaining user consent.
+
+A scope is defined in [RFC 6749 section 3.3](https://datatracker.ietf.org/doc/html/rfc6749#section-3.3)
+as a string containing a list of space-separated scope tokens.
+
+{{% boxes/note %}}
+The framework encourages the practice of obtaining additional user consent when
+a client asks for a new scope that was not granted previously. This could be
+used by future MSCs to replace the legacy [User-Interactive Authentication API](#user-interactive-authentication-api).
+{{% /boxes/note %}}
+
+##### Scope token format
+
+All scope tokens related to Matrix should start with `urn:matrix:` and use the
+`:` delimiter for further sub-division.
+
+Scope tokens related to mapping of Client-Server API access levels should start
+with `urn:matrix:client:`.
+
+{{% boxes/note %}}
+For MSCs that build on this namespace, unstable subdivisions should be used
+whilst in development. For example, if MSCXXXX wants to introduce the
+`urn:matrix:client:foo` scope, it could use
+`urn:matrix:client:com.example.mscXXXX.foo` during development.
+If it needs to introduce multiple scopes, like `urn:matrix:client:foo` and
+`urn:matrix:client:bar`, it could use
+`urn:matrix:client:com.example.mscXXXX:foo` and
+`urn:matrix:client:com.example.mscXXXX:bar`.
+{{% /boxes/note %}}
+
+##### Allocated scope tokens
+
+This specification defines the following scope tokens:
+- [`urn:matrix:client:api:*`](#full-client-server-api-readwrite-access)
+- [`urn:matrix:client:device:<device_id>`](#device-id-allocation)
+
+###### Full client-server API read/write access
+
+| Scope                     | Purpose                                     |
+|---------------------------|---------------------------------------------|
+| `urn:matrix:client:api:*` | Grants full access to the Client-Server API. |
+
+{{% boxes/note %}}
+This token matches the behavior of the legacy authentication API. Future MSCs
+could introduce more fine-grained scope tokens like
+`urn:matrix:client:api:read:*` for read-only access.
+{{% /boxes/note %}}
+
+###### Device ID allocation
+
+| Scope                                  | Purpose                                                                                      |
+|----------------------------------------|----------------------------------------------------------------------------------------------|
+| `urn:matrix:client:device:<device_id>` | Allocates the given `device_id` and associates it to the generated access and refresh tokens. |
+
+Contrary to the legacy login and registration APIs where the homeserver is
+typically the one generating a `device_id` and providing it to the client, with
+the OAuth 2.0 API, the client is responsible for allocating the `device_id`.
+
+There MUST be exactly one `urn:matrix:client:device:<device_id>` token in the
+requested scope in the login flow.
+
+When generating a new `device_id`, the client SHOULD generate a random string
+with enough entropy. It SHOULD only use characters from the unreserved character
+list defined by [RFC 3986 section 2.3](https://datatracker.ietf.org/doc/html/rfc3986#section-2.3):
+
+```
+unreserved = a-z / A-Z / 0-9 / "-" / "." / "_" / "~"
+```
+
+Using this alphabet, a 10 character string is enough to stand a sufficient
+chance of being unique per user. The homeserver MAY reject a request for a
+`device_id` that is not long enough or contains characters outside the
+unreserved list.
+
+In any case it MUST only use characters allowed by the OAuth 2.0 scope
+definition in [RFC 6749 section 3.3](https://datatracker.ietf.org/doc/html/rfc6749#section-3.3),
+which is defined as the following ASCII ranges:
+
+```
+%x21 / %x23-5B / %x5D-7E
+```
+
+This definition matches:
+- alphanumeric characters: `A-Z`, `a-z`, `0-9`
+- the following characters: ``! # $ % & ' ( ) * + , - . / : ; < = > ? @ [ ] ^ _ ` { | } ~``
+
+#### Grant types
+
+[RFC 6749](https://datatracker.ietf.org/doc/html/rfc6749) and other RFCs define
+several "grant types": ways to obtain an ["access token"](#using-access-tokens).
+
+All these grants types require the client to know the following authorization
+server metadata:
+- `token_endpoint`
+- `grant_types_supported`
+
+The client must also have obtained a `client_id` by registering with the server.
+
+This specification supports the following grant types:
+- [Authorization code grant](#authorization-code-grant)
+- [Refresh token grant](#refresh-token-grant)
+
+##### Authorization code grant
+
+As per [RFC 6749 section 4.1](https://datatracker.ietf.org/doc/html/rfc6749#section-4.1),
+the authorization code grant lets the client obtain an access token through a
+browser redirect.
+
+This grant requires the client to know the following authorization server
+metadata:
+- `authorization_endpoint`
+- `response_types_supported`
+- `response_mode_supported`
+
+To use this grant, homeservers and clients MUST:
+
+- Support the authorization code grant as per [RFC 6749 section 4.1](https://datatracker.ietf.org/doc/html/rfc6749#section-4.1).
+- Support the [refresh token grant](#refresh-token-grant).
+- Support PKCE using the `S256` code challenge method as per [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636).
+- Use pre-registered, strict redirect URIs.
+- Use the `fragment` response mode as per [OAuth 2.0 Multiple Response Type
+  Encoding Practices](https://openid.net/specs/oauth-v2-multiple-response-types-1_0.html)
+  for clients with an HTTPS redirect URI.
+
+###### User registration
+
+Clients can signal to the server that the user desires to register a new account
+by initiating the authorization code grant with the `prompt=create` parameter
+set in the authorization request as defined in [Initiating User Registration via
+OpenID Connect 1.0](https://openid.net/specs/openid-connect-prompt-create-1_0.html).
+
+Whether the homeserver supports this parameter is advertised by the
+`prompt_values_supported` authorization server metadata.
+
+Servers that support this parameter SHOULD show the account registration UI in
+the browser.
+
+##### Refresh token grant
+
+As per [RFC 6749 section 6](https://datatracker.ietf.org/doc/html/rfc6749#section-6),
+the refresh token grant lets the client exchange a refresh token for an access
+token.
+
+When authorization is granted to a client, the homeserver MUST issue a refresh
+token to the client in addition to the access token.
+
+The access token MUST be short-lived and SHOULD be refreshed using the
+`refresh_token` when expired.
+
+The homeserver SHOULD issue a new refresh token each time an old one is used,
+and invalidate the old one. However, it MUST ensure that the client is able to
+retry the refresh request in the case that the response to the request is lost.
+
+The homeserver SHOULD consider that the session is compromised if an old,
+invalidated refresh token is used, and SHOULD revoke the session.
+
+The client MUST handle access token refresh failures as follows:
+
+ - If the refresh fails due to network issues or a `5xx` HTTP status code from
+   the server, the client should retry the request with the old refresh token
+   later.
+ - If the refresh fails due to a `4xx` HTTP status code from the server, the
+   client should consider the session logged out.
+
+#### Login flow
+
+Logging in with the OAuth 2.0 API should be done with the [authorization code
+grant](#authorization-code-grant). In the context of the Matrix specification,
+this means requesting a [scope](#scope) including full client-server API
+read/write access and allocating a device ID.
+
+First, the client needs to generate the following values:
+
+- `device_id`: a unique identifier for this device; see the
+  [`urn:matrix:client:device:<device_id>`] scope.
+- `state`: a unique opaque identifier, like a [transaction ID](#transaction-identifiers),
+  that will allow the client to maintain state between the authorization request
+  and the callback.
+- `code_verifier`: a cryptographically random value that will allow to make sure
+  that the client that makes the token request for a given `code` is the same
+  one that made the authorization request.
+
+  It is defined in [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636) as
+  a high-entropy cryptographic random string using the characters `[A-Z]`,
+  `[a-z]`, `[0-9]`, `-`, `.`, `_` and `~` with a minimum length of 43 characters
+  and a maximum length of 128 characters.
+
+**Authorization request**
+
+The client then constructs the authorization request URL using the
+`authorization_endpoint` value, with the following query parameters:
+
+| Parameter               | Value                                              |
+|-------------------------|----------------------------------------------------|
+| `response_type`         | `code`                                             |
+| `client_id`             | The client ID returned from client registration.   |
+| `redirect_uri`          | The redirect URI that MUST match one of the values registered in the client metadata |
+| `scope`                 | `urn:matrix:client:api:* urn:matrix:client:device:<device_id>` with the `device_id` generated previously. |
+| `state`                 | The `state` value generated previously.            |
+| `response_mode`         | `fragment` or `query` (see "[Callback](#callback)" below). |
+| `code_challenge`        | Computed from the `code_verifier` value generated previously using the SHA-256 algorithm, as described in [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636) |
+| `code_challenge_method` | `S256`                                             |
+
+This authorization request URL must be opened in the user's browser:
+
+- For web-based clients, this can be done through a redirection or by opening
+  the URL in a new tab.
+- For native clients, this can be done by opening the URL using the system
+  browser, or, when available, through platform-specific APIs such as
+  [`ASWebAuthenticationSession`](https://developer.apple.com/documentation/authenticationservices/aswebauthenticationsession)
+  on iOS or [Android Custom Tabs](https://developer.chrome.com/docs/android/custom-tabs).
+
+Sample authorization request, with extra whitespaces for readability:
+
+```
+https://account.example.com/oauth2/auth?
+    client_id     = s6BhdRkqt3 &
+    response_type = code &
+    response_mode = fragment &
+    redirect_uri  = https://app.example.com/oauth2-callback &
+    scope         = urn:matrix:client:api:* urn:matrix:client:device:AAABBBCCCDDD &
+    state         = ewubooN9weezeewah9fol4oothohroh3 &
+    code_challenge        = 72xySjpngTcCxgbPfFmkPHjMvVDl2jW1aWP7-J6rmwU &
+    code_challenge_method = S256
+```
+
+<a id="callback"></a> **Callback**
+
+Once completed, the user is redirected to the `redirect_uri`, with either a
+successful or failed authorization in the URL fragment or query parameters.
+Whether the parameters are in the URL fragment or query parameters is determined
+by the `response_mode` value:
+
+- If set to `fragment`, the parameters will be placed in the URL fragment, like
+  `https://example.com/callback#param1=value1&param2=value2`.
+- If set to `query`, the parameters will be in placed the query string, like
+  `com.example.app:/callback?param1=value1&param2=value2`.
+
+To avoid disclosing the parameters to the web server hosting the `redirect_uri`,
+clients SHOULD use the `fragment` response mode if the `redirect_uri` is an
+HTTPS URI with a remote host.
+
+In both success and failure cases, the parameters will include the `state` value
+used in the authorization request.
+
+A successful authorization will have a `code` value, for example:
+
+```
+https://app.example.com/oauth2-callback#state=ewubooN9weezeewah9fol4oothohroh3&code=iuB7Eiz9heengah1joh2ioy9ahChuP6R
+```
+
+A failed authorization will have the following values:
+
+- `error`: the error code
+- `error_description`: the error description (optional)
+- `error_uri`: the URI where the user can find more information about the error (optional)
+
+For example:
+
+```
+https://app.example.com/oauth2-callback#state=ewubooN9weezeewah9fol4oothohroh3&error=access_denied&error_description=The+resource+owner+or+authorization+server+denied+the+request.&error_uri=https%3A%2F%2Ferrors.example.com%2F
+```
+
+**Token request**
+
+The client then exchanges the authorization code to obtain an access token using
+the token endpoint.
+
+This is done by making a POST request to the `token_endpoint` with the following
+parameters, encoded as `application/x-www-form-urlencoded` in the body:
+
+| Parameter       | Value                                                      |
+|-----------------|------------------------------------------------------------|
+| `grant_type`    | `authorization_code`                                       |
+| `code`          | The value of `code` obtained from the callback.            |
+| `redirect_uri`  | The same `redirect_uri` used in the authorization request. |
+| `client_id`     | The client ID returned from client registration.           |
+| `code_verifier` | The value generated at the start of the authorization flow. |
+
+The server replies with a JSON object containing the access token, the token
+type, the expiration time, and the refresh token.
+
+Sample token request:
+
+```
+POST /oauth2/token HTTP/1.1
+Host: account.example.com
+Content-Type: application/x-www-form-urlencoded
+Accept: application/json
+
+grant_type=authorization_code
+  &code=iuB7Eiz9heengah1joh2ioy9ahChuP6R
+  &redirect_uri=https://app.example.com/oauth2-callback
+  &client_id=s6BhdRkqt3
+  &code_verifier=ogie4iVaeteeKeeLaid0aizuimairaCh
+```
+
+Sample response:
+
+```json
+{
+  "access_token": "2YotnFZFEjr1zCsicMWpAA",
+  "token_type": "Bearer",
+  "expires_in": 299,
+  "refresh_token": "tGz3JOkF0XG5Qx2TlKWIA",
+  "scope": "urn:matrix:client:api:* urn:matrix:client:device:AAABBBCCCDDD"
+}
+```
+
+Finally, the client can call the  [`/whoami`](#get_matrixclientv3accountwhoami)
+endpoint to get the user ID that owns the access token.
+
+#### Token refresh flow
+
+Refreshing a token with the OAuth 2.0 API should be done with the [refresh token
+grant](#refresh-token-grant).
+
+When the access token expires, the client must refresh it by making a `POST`
+request to the `token_endpoint` with the following parameters, encoded as
+`application/x-www-form-urlencoded` in the body:
+
+| Parameter       | Value                                                      |
+|-----------------|------------------------------------------------------------|
+| `grant_type`    | `refresh_token`                                            |
+| `refresh_token` | The `refresh_token` obtained from the token response during the last token request. |
+| `client_id`     | The client ID returned from client registration.           |
+
+The server replies with a JSON object containing the new access token, the token
+type, the expiration time, and a new refresh token, like in the authorization
+flow.
+
 ### Account moderation
 
 #### Account locking

data/api/client-server/definitions/key_backup_session_data.yaml

@@ -23,6 +23,7 @@ properties:
     type: string
     description: |-
       The end-to-end message encryption algorithm that the key is for. Must be `m.megolm.v1.aes-sha2`.
+    example: "m.megolm.v1.aes-sha2"
   forwarding_curve25519_key_chain:
     type: array
     items:
@@ -30,31 +31,24 @@ properties:
     description: |-
       Chain of Curve25519 keys through which this session was forwarded, via [m.forwarded_room_key](/client-server-api/#mforwarded_room_key)
       events.
+    example: [ "hPQNcabIABgGnx3/ACv/jmMmiQHoeFfuLB17tzWp6Hw" ]
   sender_key:
     type: string
     description: |-
       Unpadded base64-encoded device Curve25519 key.
+    example: "RF3s+E7RkTQTGF2d8Deol0FkQvgII2aJDf3/Jp5mxVU"
   sender_claimed_keys:
     type: object
     additionalProperties:
       type: string
     description: |-
       A map from algorithm name (`ed25519`) to the Ed25519 signing key of the sending device.
+    example: { "ed25519": "aj40p+aw64yPIdsxoog8jhPu9i7l7NcFRecuOQblE3Y" }
   session_key:
     type: string
     description: |-
       Unpadded base64-encoded session key in [session-export format](https://gitlab.matrix.org/matrix-org/olm/blob/master/docs/megolm.md#session-export-format).
-example: {
+    example: "AgAAAADxKHa9uFxcXzwYoNueL5Xqi69IkD4sni8Llf..."
-  "algorithm": "m.megolm.v1.aes-sha2",
-  "forwarding_curve25519_key_chain": [
-    "hPQNcabIABgGnx3/ACv/jmMmiQHoeFfuLB17tzWp6Hw"
-  ],
-  "sender_key": "RF3s+E7RkTQTGF2d8Deol0FkQvgII2aJDf3/Jp5mxVU",
-  "sender_claimed_keys": {
-    "ed25519": "aj40p+aw64yPIdsxoog8jhPu9i7l7NcFRecuOQblE3Y",
-  },
-  "session_key": "AgAAAADxKHa9uFxcXzwYoNueL5Xqi69IkD4sni8Llf..."
-}
 required:
   - algorithm
   - forwarding_curve25519_key_chain

data/api/client-server/oauth_server_metadata.yaml

@@ -0,0 +1,176 @@
+# Copyright 2025 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+openapi: 3.1.0
+info:
+  title: Matrix Client-Server OAuth 2.0 Server Metadata Discovery API
+  version: 1.0.0
+paths:
+  "/auth_metadata":
+    get:
+      summary: Get the OAuth 2.0 authorization server metadata.
+      description: |-
+        Gets the OAuth 2.0 authorization server metadata, as defined in
+        [RFC 8414](https://datatracker.ietf.org/doc/html/rfc8414), including the
+        endpoint URLs and the supported parameters that can be used by the
+        clients.
+
+        This endpoint definition includes only the fields that are meaningful in
+        the context of the Matrix specification. The full list of possible
+        fields is available in the [OAuth Authorization Server Metadata
+        registry](https://www.iana.org/assignments/oauth-parameters/oauth-parameters.xhtml#authorization-server-metadata),
+        and normative definitions of them are available in their respective
+        RFCs.
+
+        {{% boxes/note %}}
+        The authorization server metadata is relatively large and may change
+        over time. Clients should:
+
+        - Cache the metadata appropriately based on HTTP caching headers
+        - Refetch the metadata if it is stale
+        {{% /boxes/note %}}
+      operationId: getAuthMetadata
+      responses:
+        "200":
+          description: The OAuth 2.0 authorization server metadata.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  issuer:
+                    type: string
+                    format: uri
+                    description: |-
+                      The authorization server's issuer identifier, which is a URL that uses the
+                      `https` scheme and has no query or fragment components.
+
+                      This is not used in the context of the Matrix specification, but is required
+                      by [RFC 8414](https://datatracker.ietf.org/doc/html/rfc8414).
+                  authorization_endpoint:
+                    type: string
+                    format: uri
+                    description: |-
+                      URL of the authorization endpoint, necessary to use the authorization code
+                      grant.
+                  token_endpoint:
+                    type: string
+                    format: uri
+                    description: |-
+                      URL of the token endpoint, necessary to use the authorization code grant and
+                      the refresh token grant.
+                  revocation_endpoint:
+                    type: string
+                    format: uri
+                    description: |-
+                      URL of the revocation endpoint, necessary to log out a client by invalidating
+                      its access and refresh tokens.
+                  registration_endpoint:
+                    type: string
+                    format: uri
+                    description: |-
+                      URL of the client registration endpoint, necessary to perform dynamic
+                      registration of a client.
+                  response_types_supported:
+                    type: array
+                    description: |-
+                      List of OAuth 2.0 response type strings that the server supports at the
+                      authorization endpoint.
+
+                      This array MUST contain at least the `code` value, for clients to be able to
+                      use the authorization code grant.
+                    items:
+                      type: string
+                      description: A response type that the server supports.
+                  grant_types_supported:
+                    type: array
+                    description: |-
+                      List of OAuth 2.0 grant type strings that the server supports at the token
+                      endpoint.
+
+                      This array MUST contain at least the `authorization_code` and `refresh_token`
+                      values, for clients to be able to use the authorization code grant and refresh
+                      token grant, respectively.
+                    items:
+                      type: string
+                      description: A grant type that the server supports.
+                  response_modes_supported:
+                    type: array
+                    description: |-
+                      List of OAuth 2.0 response mode strings that the server supports at the
+                      authorization endpoint.
+
+                      This array MUST contain at least the `query` and `fragment` values, for
+                      improved security in the authorization code grant.
+                    items:
+                      type: string
+                      description: A response mode that the server supports.
+                  code_challenge_methods_supported:
+                    type: array
+                    description: |-
+                      List of OAuth 2.0 Proof Key for Code Exchange (PKCE) code challenge methods
+                      that the server supports at the authorization endpoint.
+
+                      This array MUST contain at least the `S256` value, for improved security in
+                      the authorization code grant.
+                    items:
+                      type: string
+                      description: A PKCE code challenge method that the server supports.
+                  prompt_values_supported:
+                    type: array
+                    description: |-
+                      List of OpenID Connect prompt values that the server supports at the
+                      authorization endpoint.
+
+                      Only the `create` value defined in [Initiating User Registration via OpenID
+                      Connect](https://openid.net/specs/openid-connect-prompt-create-1_0.html) is
+                      supported, for a client to signal to the server that the user desires to
+                      register a new account.
+                    items:
+                      type: string
+                      description: A prompt value that the server supports.
+                required:
+                  - issuer
+                  - authorization_endpoint
+                  - token_endpoint
+                  - revocation_endpoint
+                  - registration_endpoint
+                  - response_types_supported
+                  - grant_types_supported
+                  - response_modes_supported
+                  - code_challenge_methods_supported
+                example: {
+                  "issuer": "https://account.example.com/",
+                  "authorization_endpoint": "https://account.example.com/oauth2/auth",
+                  "token_endpoint": "https://account.example.com/oauth2/token",
+                  "registration_endpoint": "https://account.example.com/oauth2/clients/register",
+                  "revocation_endpoint": "https://account.example.com/oauth2/revoke",
+                  "response_types_supported": ["code"],
+                  "grant_types_supported": ["authorization_code", "refresh_token"],
+                  "response_modes_supported": ["query", "fragment"],
+                  "code_challenge_methods_supported": ["S256"],
+                }
+      tags:
+        - Session management
+servers:
+  - url: "{protocol}://{hostname}{basePath}"
+    variables:
+      protocol:
+        enum:
+          - http
+          - https
+        default: https
+      hostname:
+        default: localhost:8008
+      basePath:
+        default: /_matrix/client/v1