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Add OAuth 2.0 authorization code and refresh token grant types (#2150)
As per MSC2964 Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>
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changelogs/client_server/newsfragments/2150.feature
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changelogs/client_server/newsfragments/2150.feature
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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.
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@ -1481,6 +1481,174 @@ MAY reject weak passwords with an error code `M_WEAK_PASSWORD`.
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### OAuth 2.0 API
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### OAuth 2.0 API
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#### Login flow
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Logging in with the OAuth 2.0 API should be done with the [authorization code
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grant](#authorization-code-grant). In the context of the Matrix specification,
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this means requesting a [scope](#scope) including full client-server API
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read/write access and allocating a device ID.
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Once the client has retrieved the [server metadata](#server-metadata-discovery),
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it needs to generate the following values:
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- `device_id`: a unique identifier for this device; see the
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[`urn:matrix:client:device:<device_id>`](#device-id-allocation) scope token.
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- `state`: a unique opaque identifier, like a [transaction ID](#transaction-identifiers),
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that will allow the client to maintain state between the authorization request
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and the callback.
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- `code_verifier`: a cryptographically random value that will allow to make sure
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that the client that makes the token request for a given `code` is the same
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one that made the authorization request.
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It is defined in [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636) as
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a high-entropy cryptographic random string using the characters `[A-Z]`,
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`[a-z]`, `[0-9]`, `-`, `.`, `_` and `~` with a minimum length of 43 characters
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and a maximum length of 128 characters.
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**Authorization request**
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The client then constructs the authorization request URL using the
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`authorization_endpoint` value, with the following query parameters:
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| Parameter | Value |
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|-------------------------|----------------------------------------------------|
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| `response_type` | `code` |
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| `client_id` | The client ID returned from client registration. |
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| `redirect_uri` | The redirect URI that MUST match one of the values registered in the client metadata |
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| `scope` | `urn:matrix:client:api:* urn:matrix:client:device:<device_id>` with the `device_id` generated previously. |
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| `state` | The `state` value generated previously. |
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| `response_mode` | `fragment` or `query` (see "[Callback](#callback)" below). |
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| `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). |
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| `code_challenge_method` | `S256` |
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This authorization request URL must be opened in the user's browser:
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- For web-based clients, this can be done through a redirection or by opening
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the URL in a new tab.
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- For native clients, this can be done by opening the URL using the system
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browser, or, when available, through platform-specific APIs such as
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[`ASWebAuthenticationSession`](https://developer.apple.com/documentation/authenticationservices/aswebauthenticationsession)
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on iOS or [Android Custom Tabs](https://developer.chrome.com/docs/android/custom-tabs).
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Sample authorization request, with extra whitespaces for readability:
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```
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https://account.example.com/oauth2/auth?
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client_id = s6BhdRkqt3 &
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response_type = code &
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response_mode = fragment &
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redirect_uri = https://app.example.com/oauth2-callback &
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scope = urn:matrix:client:api:* urn:matrix:client:device:AAABBBCCCDDD &
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state = ewubooN9weezeewah9fol4oothohroh3 &
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code_challenge = 72xySjpngTcCxgbPfFmkPHjMvVDl2jW1aWP7-J6rmwU &
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code_challenge_method = S256
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```
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<a id="callback"></a> **Callback**
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Once completed, the user is redirected to the `redirect_uri`, with either a
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successful or failed authorization in the URL fragment or query parameters.
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Whether the parameters are in the URL fragment or query parameters is determined
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by the `response_mode` value:
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- If set to `fragment`, the parameters will be placed in the URL fragment, like
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`https://example.com/callback#param1=value1¶m2=value2`.
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- If set to `query`, the parameters will be in placed the query string, like
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`com.example.app:/callback?param1=value1¶m2=value2`.
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To avoid disclosing the parameters to the web server hosting the `redirect_uri`,
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clients SHOULD use the `fragment` response mode if the `redirect_uri` is an
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HTTPS URI with a remote host.
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In both success and failure cases, the parameters will include the `state` value
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used in the authorization request.
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A successful authorization will have a `code` value, for example:
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```
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https://app.example.com/oauth2-callback#state=ewubooN9weezeewah9fol4oothohroh3&code=iuB7Eiz9heengah1joh2ioy9ahChuP6R
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```
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A failed authorization will have the following values:
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- `error`: the error code
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- `error_description`: the error description (optional)
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- `error_uri`: the URI where the user can find more information about the error (optional)
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For example:
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```
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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
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```
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**Token request**
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The client then exchanges the authorization code to obtain an access token using
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the token endpoint.
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This is done by making a POST request to the `token_endpoint` with the following
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parameters, encoded as `application/x-www-form-urlencoded` in the body:
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| Parameter | Value |
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|-----------------|------------------------------------------------------------|
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| `grant_type` | `authorization_code` |
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| `code` | The value of `code` obtained from the callback. |
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| `redirect_uri` | The same `redirect_uri` used in the authorization request. |
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| `client_id` | The client ID returned from client registration. |
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| `code_verifier` | The value generated at the start of the authorization flow. |
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The server replies with a JSON object containing the access token, the token
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type, the expiration time, and the refresh token.
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Sample token request:
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```
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POST /oauth2/token HTTP/1.1
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Host: account.example.com
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Content-Type: application/x-www-form-urlencoded
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Accept: application/json
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grant_type=authorization_code
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&code=iuB7Eiz9heengah1joh2ioy9ahChuP6R
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&redirect_uri=https://app.example.com/oauth2-callback
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&client_id=s6BhdRkqt3
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&code_verifier=ogie4iVaeteeKeeLaid0aizuimairaCh
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```
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Sample response:
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```json
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{
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"access_token": "2YotnFZFEjr1zCsicMWpAA",
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"token_type": "Bearer",
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"expires_in": 299,
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"refresh_token": "tGz3JOkF0XG5Qx2TlKWIA",
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"scope": "urn:matrix:client:api:* urn:matrix:client:device:AAABBBCCCDDD"
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}
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```
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Finally, the client can call the [`/whoami`](#get_matrixclientv3accountwhoami)
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endpoint to get the user ID that owns the access token.
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#### Token refresh flow
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Refreshing a token with the OAuth 2.0 API should be done with the [refresh token
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grant](#refresh-token-grant).
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When the access token expires, the client must refresh it by making a `POST`
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request to the `token_endpoint` with the following parameters, encoded as
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`application/x-www-form-urlencoded` in the body:
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| Parameter | Value |
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|-----------------|------------------------------------------------------------|
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| `grant_type` | `refresh_token` |
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| `refresh_token` | The `refresh_token` obtained from the token response during the last token request. |
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| `client_id` | The client ID returned from client registration. |
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The server replies with a JSON object containing the new access token, the token
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type, the expiration time, and a new refresh token, like in the authorization
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flow.
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#### Server metadata discovery
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#### Server metadata discovery
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{{% http-api spec="client-server" api="oauth_server_metadata" %}}
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{{% http-api spec="client-server" api="oauth_server_metadata" %}}
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@ -1778,6 +1946,84 @@ This definition matches:
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- alphanumeric characters: `A-Z`, `a-z`, `0-9`
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- alphanumeric characters: `A-Z`, `a-z`, `0-9`
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- the following characters: ``! # $ % & ' ( ) * + , - . / : ; < = > ? @ [ ] ^ _ ` { | } ~``
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- the following characters: ``! # $ % & ' ( ) * + , - . / : ; < = > ? @ [ ] ^ _ ` { | } ~``
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#### Grant types
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[RFC 6749](https://datatracker.ietf.org/doc/html/rfc6749) and other RFCs define
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several "grant types": ways to obtain an ["access token"](#using-access-tokens).
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All these grants types require the client to know the following [authorization
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server metadata](#server-metadata-discovery):
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- `token_endpoint`
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- `grant_types_supported`
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The client must also have obtained a `client_id` by [registering with the server](#client-registration).
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This specification supports the following grant types:
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- [Authorization code grant](#authorization-code-grant)
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- [Refresh token grant](#refresh-token-grant)
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##### Authorization code grant
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As per [RFC 6749 section 4.1](https://datatracker.ietf.org/doc/html/rfc6749#section-4.1),
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the authorization code grant lets the client obtain an access token through a
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browser redirect.
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This grant requires the client to know the following [authorization server
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metadata](#server-metadata-discovery):
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- `authorization_endpoint`
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- `response_types_supported`
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- `response_mode_supported`
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To use this grant, homeservers and clients MUST:
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- Support the authorization code grant as per [RFC 6749 section 4.1](https://datatracker.ietf.org/doc/html/rfc6749#section-4.1).
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- Support the [refresh token grant](#refresh-token-grant).
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- Support PKCE using the `S256` code challenge method as per [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636).
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- Use [pre-registered](#client-registration), strict redirect URIs.
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- Use the `fragment` response mode as per [OAuth 2.0 Multiple Response Type
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Encoding Practices](https://openid.net/specs/oauth-v2-multiple-response-types-1_0.html)
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for clients with an HTTPS redirect URI.
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###### User registration
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Clients can signal to the server that the user desires to register a new account
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by initiating the authorization code grant with the `prompt=create` parameter
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set in the authorization request as defined in [Initiating User Registration via
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OpenID Connect 1.0](https://openid.net/specs/openid-connect-prompt-create-1_0.html).
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Whether the homeserver supports this parameter is advertised by the
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`prompt_values_supported` authorization server metadata.
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Servers that support this parameter SHOULD show the account registration UI in
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the browser.
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##### Refresh token grant
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As per [RFC 6749 section 6](https://datatracker.ietf.org/doc/html/rfc6749#section-6),
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the refresh token grant lets the client exchange a refresh token for an access
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token.
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When authorization is granted to a client, the homeserver MUST issue a refresh
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token to the client in addition to the access token.
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The access token MUST be short-lived and SHOULD be refreshed using the
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`refresh_token` when expired.
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The homeserver SHOULD issue a new refresh token each time an old one is used,
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and invalidate the old one. However, it MUST ensure that the client is able to
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retry the refresh request in the case that the response to the request is lost.
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The homeserver SHOULD consider that the session is compromised if an old,
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invalidated refresh token is used, and SHOULD revoke the session.
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The client MUST handle access token refresh failures as follows:
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- If the refresh fails due to network issues or a `5xx` HTTP status code from
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the server, the client should retry the request with the old refresh token
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later.
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- If the refresh fails due to a `4xx` HTTP status code from the server, the
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client should consider the session logged out.
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### Account moderation
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### Account moderation
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#### Account locking
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#### Account locking
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