synapse/docs/openid.md

# Configuring Synapse to authenticate against an OpenID Connect provider

Synapse can be configured to use an OpenID Connect Provider (OP) for
authentication, instead of its own local password database.

Any OP should work with Synapse, as long as it supports the authorization code
flow. There are a few options for that:

 - start a local OP. Synapse has been tested with [Hydra][hydra] and
   [Dex][dex-idp].  Note that for an OP to work, it should be served under a
   secure (HTTPS) origin.  A certificate signed with a self-signed, locally
   trusted CA should work. In that case, start Synapse with a `SSL_CERT_FILE`
   environment variable set to the path of the CA.

 - set up a SaaS OP, like [Google][google-idp], [Auth0][auth0] or
   [Okta][okta]. Synapse has been tested with Auth0 and Google.

It may also be possible to use other OAuth2 providers which provide the
[authorization code grant type](https://tools.ietf.org/html/rfc6749#section-4.1),
such as [Github][github-idp].

[google-idp]: https://developers.google.com/identity/protocols/oauth2/openid-connect
[auth0]: https://auth0.com/
[okta]: https://www.okta.com/
[dex-idp]: https://github.com/dexidp/dex
[hydra]: https://www.ory.sh/docs/hydra/
[github-idp]: https://developer.github.com/apps/building-oauth-apps/authorizing-oauth-apps

## Preparing Synapse

The OpenID integration in Synapse uses the
[`authlib`](https://pypi.org/project/Authlib/) library, which must be installed
as follows:

 * The relevant libraries are included in the Docker images and Debian packages
   provided by `matrix.org` so no further action is needed.

 * If you installed Synapse into a virtualenv, run `/path/to/env/bin/pip
   install synapse[oidc]` to install the necessary dependencies.

 * For other installation mechanisms, see the documentation provided by the
   maintainer.

To enable the OpenID integration, you should then add an `oidc_config` section
to your configuration file (or uncomment the `enabled: true` line in the
existing section). See [sample_config.yaml](./sample_config.yaml) for some
sample settings, as well as the text below for example configurations for
specific providers.

## Sample configs

Here are a few configs for providers that should work with Synapse.

### [Dex][dex-idp]

[Dex][dex-idp] is a simple, open-source, certified OpenID Connect Provider.
Although it is designed to help building a full-blown provider with an
external database, it can be configured with static passwords in a config file.

Follow the [Getting Started
guide](https://github.com/dexidp/dex/blob/master/Documentation/getting-started.md)
to install Dex.

Edit `examples/config-dev.yaml` config file from the Dex repo to add a client:

```yaml
staticClients:
- id: synapse
  secret: secret
  redirectURIs:
  - '[synapse public baseurl]/_synapse/oidc/callback'
  name: 'Synapse'
```

Run with `dex serve examples/config-dex.yaml`.

Synapse config:

```yaml
oidc_config:
   enabled: true
   skip_verification: true # This is needed as Dex is served on an insecure endpoint
   issuer: "http://127.0.0.1:5556/dex"
   client_id: "synapse"
   client_secret: "secret"
   scopes: ["openid", "profile"]
   user_mapping_provider:
     config:
       localpart_template: "{{ user.name }}"
       display_name_template: "{{ user.name|capitalize }}"
```

### [Auth0][auth0]

1. Create a regular web application for Synapse
2. Set the Allowed Callback URLs to `[synapse public baseurl]/_synapse/oidc/callback`
3. Add a rule to add the `preferred_username` claim.
   <details>
    <summary>Code sample</summary>

    ```js
    function addPersistenceAttribute(user, context, callback) {
      user.user_metadata = user.user_metadata || {};
      user.user_metadata.preferred_username = user.user_metadata.preferred_username || user.user_id;
      context.idToken.preferred_username = user.user_metadata.preferred_username;

      auth0.users.updateUserMetadata(user.user_id, user.user_metadata)
        .then(function(){
            callback(null, user, context);
        })
        .catch(function(err){
            callback(err);
        });
    }
    ```
  </details>

Synapse config:

```yaml
oidc_config:
   enabled: true
   issuer: "https://your-tier.eu.auth0.com/" # TO BE FILLED
   client_id: "your-client-id" # TO BE FILLED
   client_secret: "your-client-secret" # TO BE FILLED
   scopes: ["openid", "profile"]
   user_mapping_provider:
     config:
       localpart_template: "{{ user.preferred_username }}"
       display_name_template: "{{ user.name }}"
```

### GitHub

GitHub is a bit special as it is not an OpenID Connect compliant provider, but
just a regular OAuth2 provider.

The [`/user` API endpoint](https://developer.github.com/v3/users/#get-the-authenticated-user)
can be used to retrieve information on the authenticated user. As the Synaspse
login mechanism needs an attribute to uniquely identify users, and that endpoint
does not return a `sub` property, an alternative `subject_claim` has to be set.

1. Create a new OAuth application: https://github.com/settings/applications/new.
2. Set the callback URL to `[synapse public baseurl]/_synapse/oidc/callback`.

Synapse config:

```yaml
oidc_config:
   enabled: true
   discover: false
   issuer: "https://github.com/"
   client_id: "your-client-id" # TO BE FILLED
   client_secret: "your-client-secret" # TO BE FILLED
   authorization_endpoint: "https://github.com/login/oauth/authorize"
   token_endpoint: "https://github.com/login/oauth/access_token"
   userinfo_endpoint: "https://api.github.com/user"
   scopes: ["read:user"]
   user_mapping_provider:
     config:
       subject_claim: "id"
       localpart_template: "{{ user.login }}"
       display_name_template: "{{ user.name }}"
```

### [Google][google-idp]

1. Set up a project in the Google API Console (see
   https://developers.google.com/identity/protocols/oauth2/openid-connect#appsetup).
2. add an "OAuth Client ID" for a Web Application under "Credentials".
3. Copy the Client ID and Client Secret, and add the following to your synapse config:
   ```yaml
   oidc_config:
     enabled: true
     issuer: "https://accounts.google.com/"
     client_id: "your-client-id" # TO BE FILLED
     client_secret: "your-client-secret" # TO BE FILLED
     scopes: ["openid", "profile"]
     user_mapping_provider:
       config:
         localpart_template: "{{ user.given_name|lower }}"
         display_name_template: "{{ user.name }}"
   ```
4. Back in the Google console, add this Authorized redirect URI: `[synapse
   public baseurl]/_synapse/oidc/callback`.

### Twitch

1. Setup a developer account on [Twitch](https://dev.twitch.tv/)
2. Obtain the OAuth 2.0 credentials by [creating an app](https://dev.twitch.tv/console/apps/)
3. Add this OAuth Redirect URL: `[synapse public baseurl]/_synapse/oidc/callback`

Synapse config:

```yaml
oidc_config:
   enabled: true
   issuer: "https://id.twitch.tv/oauth2/"
   client_id: "your-client-id" # TO BE FILLED
   client_secret: "your-client-secret" # TO BE FILLED
   client_auth_method: "client_secret_post"
   user_mapping_provider:
     config:
       localpart_template: '{{ user.preferred_username }}'
       display_name_template: '{{ user.name }}'
```