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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="../../../welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="../../../setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="../../../postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="../../../reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="../../../setup/forward_proxy.html">Configuring a Forward/Outbound Proxy</a></li><li class="chapter-item expanded "><a href="../../../turn-howto.html">Configuring a Turn Server</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../../setup/turn/coturn.html">coturn TURN server</a></li><li class="chapter-item expanded "><a href="../../../setup/turn/eturnal.html">eturnal TURN server</a></li></ol></li><li class="chapter-item expanded "><a href="../../../delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a href="../../../upgrade.html">Upgrading between Synapse Versions</a></li><li class="chapter-item expanded affix "><li class="part-title">Usage</li><li class="chapter-item expanded "><a href="../../../federate.html">Federation</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/index.html">Configuration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../../usage/configuration/config_documentation.html">Configuration Manual</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/homeserver_sample_config.html">Homeserver Sample Config File</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/logging_sample_config.html">Logging Sample Config File</a></li><li class="chapter-item expanded "><a href="../../../structured_logging.html">Structured Logging</a></li><li class="chapter-item expanded "><a href="../../../templates.html">Templates</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/user_authentication/index.html">User Authentication</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../../usage/configuration/user_authentication/single_sign_on/index.html">Single-Sign On</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../../openid.html">OpenID Connect</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/user_authentication/single_sign_on/saml.html">SAML</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/user_authentication/single_sign_on/cas.html">CAS</a></li><li class="chapter-item expanded "><a href="../../../sso_mapping_providers.html">SSO Mapping Providers</a></li></ol></li><li class="chapter-item expanded "><a href="../../../password_auth_providers.html">Password Auth Providers</a></li><li class="chapter-item expanded "><a href="../../../jwt.html">JSON Web Tokens</a></li><li class="chapter-item expanded "><a href="../../../usage/configuration/user_authentication/refresh_tokens.html" class="active">Refresh Tokens</a></li></ol></li><li class="chapter-item expanded "><a href="../../../CAPTCHA_SETUP.html">Registration Captcha</a></li><li class="chapter-item expanded "><a href="../../../application_services.html">Application Services</a></li><li class="chapter-item expanded "><a href="../../../server_notices.html">Server Notices</a></li><li class="chapter-item expanded "><a href="../../../consent_tracking.html">Consent Tracking</a></li><li class="chapter-item expanded "><a href="../../../user_directory.html">User Directory</a></li><li class="chapter-item expanded "><a href="../../../message_retention_policies.html">Message Retention Policies</a></li><li class="chapter-item expanded "><a href="../../../modules/index.html
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<h1 id="refresh-tokens"><a class="header" href="#refresh-tokens">Refresh Tokens</a></h1>
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<p>Synapse supports refresh tokens since version 1.49 (some earlier versions had support for an earlier, experimental draft of <a href="https://github.com/matrix-org/matrix-doc/blob/main/proposals/2918-refreshtokens.md#msc2918-refresh-tokens">MSC2918</a> which is not compatible).</p>
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<h2 id="background-and-motivation"><a class="header" href="#background-and-motivation">Background and motivation</a></h2>
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<p>Synapse users' sessions are identified by <strong>access tokens</strong>; access tokens are
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issued to users on login. Each session gets a unique access token which identifies
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it; the access token must be kept secret as it grants access to the user's account.</p>
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<p>Traditionally, these access tokens were eternally valid (at least until the user
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explicitly chose to log out).</p>
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<p>In some cases, it may be desirable for these access tokens to expire so that the
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potential damage caused by leaking an access token is reduced.
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On the other hand, forcing a user to re-authenticate (log in again) often might
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be too much of an inconvenience.</p>
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<p><strong>Refresh tokens</strong> are a mechanism to avoid some of this inconvenience whilst
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still getting most of the benefits of short access token lifetimes.
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Refresh tokens are also a concept present in OAuth 2 — further reading is available
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<a href="https://datatracker.ietf.org/doc/html/rfc6749#section-1.5">here</a>.</p>
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<p>When refresh tokens are in use, both an access token and a refresh token will be
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issued to users on login. The access token will expire after a predetermined amount
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of time, but otherwise works in the same way as before. When the access token is
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close to expiring (or has expired), the user's client should present the homeserver
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(Synapse) with the refresh token.</p>
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<p>The homeserver will then generate a new access token and refresh token for the user
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and return them. The old refresh token is invalidated and can not be used again*.</p>
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<p>Finally, refresh tokens also make it possible for sessions to be logged out if they
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are inactive for too long, before the session naturally ends; see the configuration
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guide below.</p>
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<p>*To prevent issues if clients lose connection half-way through refreshing a token,
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the refresh token is only invalidated once the new access token has been used at
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least once. For all intents and purposes, the above simplification is sufficient.</p>
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<h2 id="caveats"><a class="header" href="#caveats">Caveats</a></h2>
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<p>There are some caveats:</p>
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<ul>
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<li>If a third party gets both your access token and refresh token, they will be able to
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continue to enjoy access to your session.
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<ul>
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<li>This is still an improvement because you (the user) will notice when <em>your</em>
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session expires and you're not able to use your refresh token.
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That would be a giveaway that someone else has compromised your session.
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You would be able to log in again and terminate that session.
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Previously (with long-lived access tokens), a third party that has your access
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token could go undetected for a very long time.</li>
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</ul>
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</li>
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<li>Clients need to implement support for refresh tokens in order for them to be a
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useful mechanism.
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<ul>
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<li>It is up to homeserver administrators if they want to issue long-lived access
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tokens to clients not implementing refresh tokens.
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<ul>
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<li>For compatibility, it is likely that they should, at least until client support
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is widespread.
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<ul>
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<li>Users with clients that support refresh tokens will still benefit from the
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added security; it's not possible to downgrade a session to using long-lived
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access tokens so this effectively gives users the choice.</li>
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</ul>
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</li>
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<li>In a closed environment where all users use known clients, this may not be
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an issue as the homeserver administrator can know if the clients have refresh
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token support. In that case, the non-refreshable access token lifetime
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may be set to a short duration so that a similar level of security is provided.</li>
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</ul>
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</li>
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</ul>
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</li>
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</ul>
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<h2 id="configuration-guide"><a class="header" href="#configuration-guide">Configuration Guide</a></h2>
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<p>The following configuration options, in the <code>registration</code> section, are related:</p>
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<ul>
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<li><code>session_lifetime</code>: maximum length of a session, even if it's refreshed.
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In other words, the client must log in again after this time period.
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In most cases, this can be unset (infinite) or set to a long time (years or months).</li>
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<li><code>refreshable_access_token_lifetime</code>: lifetime of access tokens that are created
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by clients supporting refresh tokens.
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This should be short; a good value might be 5 minutes (<code>5m</code>).</li>
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<li><code>nonrefreshable_access_token_lifetime</code>: lifetime of access tokens that are created
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by clients which don't support refresh tokens.
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Make this short if you want to effectively force use of refresh tokens.
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Make this long if you don't want to inconvenience users of clients which don't
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support refresh tokens (by forcing them to frequently re-authenticate using
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login credentials).</li>
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<li><code>refresh_token_lifetime</code>: lifetime of refresh tokens.
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In other words, the client must refresh within this time period to maintain its session.
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Unless you want to log inactive sessions out, it is often fine to use a long
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value here or even leave it unset (infinite).
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Beware that making it too short will inconvenience clients that do not connect
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very often, including mobile clients and clients of infrequent users (by making
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it more difficult for them to refresh in time, which may force them to need to
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re-authenticate using login credentials).</li>
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</ul>
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<p><strong>Note:</strong> All four options above only apply when tokens are created (by logging in or refreshing).
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Changes to these settings do not apply retroactively.</p>
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<h3 id="using-refresh-token-expiry-to-log-out-inactive-sessions"><a class="header" href="#using-refresh-token-expiry-to-log-out-inactive-sessions">Using refresh token expiry to log out inactive sessions</a></h3>
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<p>If you'd like to force sessions to be logged out upon inactivity, you can enable
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refreshable access token expiry and refresh token expiry.</p>
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<p>This works because a client must refresh at least once within a period of
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<code>refresh_token_lifetime</code> in order to maintain valid credentials to access the
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account.</p>
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<p>(It's suggested that <code>refresh_token_lifetime</code> should be longer than
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<code>refreshable_access_token_lifetime</code> and this section assumes that to be the case
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for simplicity.)</p>
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<p>Note: this will only affect sessions using refresh tokens. You may wish to
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set a short <code>nonrefreshable_access_token_lifetime</code> to prevent this being bypassed
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by clients that do not support refresh tokens.</p>
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<h4 id="choosing-values-that-guarantee-permitting-some-inactivity"><a class="header" href="#choosing-values-that-guarantee-permitting-some-inactivity">Choosing values that guarantee permitting some inactivity</a></h4>
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<p>It may be desirable to permit some short periods of inactivity, for example to
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accommodate brief outages in client connectivity.</p>
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<p>The following model aims to provide guidance for choosing <code>refresh_token_lifetime</code>
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and <code>refreshable_access_token_lifetime</code> to satisfy requirements of the form:</p>
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<ol>
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<li>inactivity longer than <code>L</code> <strong>MUST</strong> cause the session to be logged out; and</li>
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<li>inactivity shorter than <code>S</code> <strong>MUST NOT</strong> cause the session to be logged out.</li>
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</ol>
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<p>This model makes the weakest assumption that all active clients will refresh as
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needed to maintain an active access token, but no sooner.
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<em>In reality, clients may refresh more often than this model assumes, but the
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above requirements will still hold.</em></p>
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<p>To satisfy the above model,</p>
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<ul>
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<li><code>refresh_token_lifetime</code> should be set to <code>L</code>; and</li>
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<li><code>refreshable_access_token_lifetime</code> should be set to <code>L - S</code>.</li>
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</ul>
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</main>
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