Merge f7c1672959 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/2148.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/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/2154.clarification

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

content/client-server-api/_index.md

@@ -1481,6 +1481,303 @@ 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" %}}
+
+#### Client registration
+
+Before being able to use the authorization flow to obtain an access token, a
+client needs to obtain a `client_id` by registering itself with the server.
+
+This should be done via OAuth 2.0 Dynamic Client Registration as defined in
+[RFC 7591](https://datatracker.ietf.org/doc/html/rfc7591).
+
+##### Client metadata
+
+In OAuth 2.0, clients register a set of metadata values with the authorization
+server, which associates it with a newly generated `client_id`. These values are
+used to describe the client to the user and define how the client interacts with
+the server.
+
+{{% definition path="schemas/oauth2-client-metadata" %}}
+
+###### Metadata localization
+
+As per [RFC 7591 section 2.2](https://tools.ietf.org/html/rfc7591#section-2.2),
+all the human-readable metadata values MAY be localized.
+
+The human-readable values include:
+- `client_name`
+- `logo_uri`
+- `tos_uri`
+- `policy-uri`
+
+For example:
+
+```json
+{
+  "client_name": "Digital mailbox",
+  "client_name#en-US": "Digital mailbox",
+  "client_name#en-GB": "Digital postbox",
+  "client_name#fr": "Boîte aux lettres numérique",
+  "tos_uri": "https://example.com/tos.html",
+  "tos_uri#fr": "https://example.com/fr/tos.html",
+  "policy_uri": "https://example.com/policy.html",
+  "policy_uri#fr": "https://example.com/fr/policy.html"
+}
+```
+
+###### Redirect URI validation
+
+The redirect URI plays a critical role in validating the authenticity of the
+client. The client "proves" its identity by demonstrating that it controls the
+redirect URI. This is why it is critical to have strict validation of the
+redirect URI.
+
+The `application_type` metadata is used to determine the type of client.
+
+In all cases, the redirect URI MUST NOT have a fragment component.
+
+**Web clients**
+
+`web` clients can use redirect URIs that:
+
+- MUST use the `https` scheme.
+- MUST NOT use a user or password in the authority component of the URI.
+- MUST use the client URI as a common base for the authority component, as
+  defined previously.
+- MAY include an `application/x-www-form-urlencoded` formatted query component.
+
+For example, with `https://example.com/` as the client URI, the following are
+valid redirect URIs:
+- `https://example.com/callback`
+- `https://app.example.com/callback`
+- `https://example.com:5173/?query=value`
+
+With the same client URI, the following are invalid redirect URIs:
+- `https://example.com/callback#fragment`
+- `http://example.com/callback`
+- `http://localhost/`
+
+**Native clients**
+
+`native` clients can use three types of redirect URIs:
+
+1. **Private-Use URI Scheme**
+    - The scheme MUST be prefixed with the client URI hostname in reverse-DNS
+      notation. For example, if the client URI is `https://example.com/`, then a
+      valid custom URI scheme would be `com.example.app:/`.
+    - There MUST NOT be an authority component. This means that the URI MUST have
+      either a single slash or none immediately following the scheme, with no
+      hostname, username, or port.
+2. **`http` URI on the loopback interface**
+    - The scheme MUST be `http`.
+    - The host part MUST be `localhost`, `127.0.0.1`, or `[::1]`.
+    - There MUST NOT be a port. The homeserver MUST then accept any port number
+      during the authorization flow.
+3. **Claimed `https` Scheme URI**
+
+    Some operating systems allow apps to claim `https` scheme URIs in the
+    domains they control. When the browser encounters a claimed URI, instead of
+    the page being loaded in the browser, the native app is launched with the
+    URI supplied as a launch parameter. The same rules as for `web` clients
+    apply.
+
+These restrictions are the same as defined by [RFC 8252 section 7](https://tools.ietf.org/html/rfc8252#section-7).
+
+For example, with `https://example.com/` as the client URI,
+
+These are valid redirect URIs:
+- `com.example.app:/callback`
+- `com.example:/`
+- `com.example:callback`
+- `http://localhost/callback`
+- `http://127.0.0.1/callback`
+- `http://[::1]/callback`
+
+These are invalid redirect URIs:
+- `example:/callback`
+- `com.example.app://callback`
+- `https://localhost/callback`
+- `http://localhost:1234/callback`
+
+##### Dynamic client registration flow
+
+To register, the client sends an HTTP `POST` request to the
+`registration_endpoint`, which can be found in the server metadata. The body of
+the request is the JSON-encoded [`OAuthClientMetadata`](#client-metadata).
+
+For example, the client could send the following registration request:
+
+```http
+POST /register HTTP/1.1
+Content-Type: application/json
+Accept: application/json
+Server: auth.example.com
+```
+
+```json
+{
+  "client_name": "My App",
+  "client_name#fr": "Mon application",
+  "client_uri": "https://example.com/",
+  "logo_uri": "https://example.com/logo.png",
+  "tos_uri": "https://example.com/tos.html",
+  "tos_uri#fr": "https://example.com/fr/tos.html",
+  "policy_uri": "https://example.com/policy.html",
+  "policy_uri#fr": "https://example.com/fr/policy.html",
+  "redirect_uris": ["https://app.example.com/callback"],
+  "token_endpoint_auth_method": "none",
+  "response_types": ["code"],
+  "grant_types": [
+    "authorization_code",
+    "refresh_token",
+    "urn:ietf:params:oauth:grant-type:token-exchange"
+  ],
+  "application_type": "web"
+}
+```
+
+Upon successful registration, the server replies with an `HTTP 201 Created`
+response, with a JSON object containing the allocated `client_id` and all the
+registered metadata values.
+
+With the registration request above, the server might reply with:
+
+```json
+{
+  "client_id": "s6BhdRkqt3",
+  "client_name": "My App",
+  "client_uri": "https://example.com/",
+  "logo_uri": "https://example.com/logo.png",
+  "tos_uri": "https://example.com/tos.html",
+  "policy_uri": "https://example.com/policy.html",
+  "redirect_uris": ["https://app.example.com/callback"],
+  "token_endpoint_auth_method": "none",
+  "response_types": ["code"],
+  "grant_types": ["authorization_code", "refresh_token"],
+  "application_type": "web"
+}
+```
+
+In this example, the server has not registered the locale-specific values for
+`client_name`, `tos_uri`, and `policy_uri`, which is why they are not present in
+the response. The server also does not support the
+`urn:ietf:params:oauth:grant-type:token-exchange` grant type, which is why it is
+not present in the response.
+
+The client MUST store the `client_id` for future use.
+
+To avoid the number of client registrations growing over time, the server MAY
+choose to delete client registrations that don't have an active session. The
+server MUST NOT delete client registrations that have an active session.
+
+Clients MUST perform a new client registration at the start of each
+authorization flow.
+
+{{% boxes/note %}}
+Because each client on each user device will do its own registration, they may
+all have different `client_id`s. This means that the server may store the same
+client registration multiple times, which could lead to a large number of client
+registrations.
+
+This can be mitigated by de-duplicating client registrations that have identical
+metadata. By doing so, different users on different devices using the same
+client can share a single `client_id`, reducing the overall number of
+registrations.
+{{% /boxes/note %}}
+
+#### 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: ``! # $ % & ' ( ) * + , - . / : ; < = > ? @ [ ] ^ _ ` { | } ~``
+
 ### 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

data/schemas/oauth2-client-metadata.yaml

@@ -0,0 +1,140 @@
+# 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.
+title: OAuthClientMetadata
+type: object
+description: |-
+  This definition of the metadata specifies only the fields that are meaningful
+  in the context of the Matrix specification. All the possible values are
+  registered in the [OAuth Dynamic Client Registration Metadata registry](https://www.iana.org/assignments/oauth-parameters/oauth-parameters.xhtml#client-metadata),
+  and normative definitions of them are available in their respective RFCs.
+properties:
+  client_uri:
+    type: string
+    format: uri
+    description: |-
+      A URL to a valid web page that SHOULD give the user more information about
+      the client.
+
+      This URL MUST use the `https` scheme and SHOULD NOT require authentication
+      to access. It MUST NOT use a user or password in the authority component
+      of the URI.
+
+      The server MAY reject client registrations if this field is invalid or
+      missing.
+
+      This URI is a common base for all the other URIs in the metadata: those
+      MUST be either on the same host or on a subdomain of the host of the
+      `client_uri`. The port number, path and query components MAY be different.
+
+      For example, if the `client_uri` is `https://example.com/`, then one of
+      the `redirect_uris` can be `https://example.com/callback` or
+      `https://app.example.com/callback`, but not `https://app.com/callback`.
+  client_name:
+    type: string
+    description: |-
+      Human-readable name of the client to be presented to the user.
+
+      This field can be [localized](/client-server-api/#metadata-localization).
+  logo_uri:
+    type: string
+    format: uri
+    description: |-
+      URL that references a logo for the client.
+
+      This URL MUST use the `https` scheme.
+
+      This field can be [localized](/client-server-api/#metadata-localization).
+  tos_uri:
+    type: string
+    format: uri
+    description: |-
+      URL that points to a human-readable terms of service document for the
+      client.
+
+      This URL MUST use the `https` scheme and SHOULD NOT require authentication
+      to access. It MUST NOT use a user or password in the authority component
+      of the URI.
+
+      If this field is set, the server SHOULD show or link to this URL.
+
+      This field can be [localized](/client-server-api/#metadata-localization).
+  policy_uri:
+    type: string
+    format: uri
+    description: |-
+      URL that points to a human-readable policy document for the client.
+
+      This URL MUST use the `https` scheme and SHOULD NOT require authentication
+      to access. It MUST NOT use a user or password in the authority component
+      of the URI.
+
+      If this field is set, the server SHOULD show or link to this URL.
+
+      This field can be [localized](/client-server-api/#metadata-localization).
+  redirect_uris:
+    type: array
+    description: |-
+      Array of redirection URIs for use in redirect-based flows.
+
+      At least one URI is required to use the authorization code grant.
+
+      The server MUST perform [validation on redirect URIs](/client-server-api/#redirect-uri-validation).
+    items:
+      type: string
+      format: uri
+      description: A redirection URI.
+  response_types:
+    type: array
+    description: |-
+      Array of the OAuth 2.0 response types that the client may use.
+
+      This MUST include the `code` value to use the authorization code grant.
+
+      The server MUST ignore values that it does not understand.
+    items:
+      type: string
+      description: A response type that the client may use.
+  grant_types:
+    type: array
+    description: |-
+      Array of the OAuth 2.0 grant types that the client may use.
+
+      This MUST include:
+      - the `authorization_code` value to use the authorization code grant,
+      - the `refresh_token` value to use the refresh token grant.
+
+      The server MUST ignore values that it does not understand.
+    items:
+      type: string
+      description: A grant type that the client may use.
+  token_endpoint_auth_method:
+    type: string
+    description: |-
+      String indicator of the requested authentication method for the token
+      endpoint.
+
+      The homeserver MUST support the `none` value, as most Matrix clients are
+      client-side only, do not have a server component, and therefore are public
+      clients.
+  application_type:
+    type: string
+    description: |-
+      Kind of the application.
+
+      The homeserver MUST support the `web` and `native` values to be able to
+      perform [redirect URI validation](/client-server-api/#redirect-uri-validation).
+
+      Defaults to `web` if omitted.
+required:
+  - client_uri