Update docs on how to use synapse & keycloak OIDC

Use up-to-date example from synapse docs

Add link to keycloak website

Add link to synapse docs on OIDC

docs/configuring-playbook-synapse.md

@@ -56,21 +56,27 @@ Certain Synapse administration tasks (managing users and rooms, etc.) can be per
 
 If you'd like to use OpenID Connect authentication with Synapse, you'll need some additional reverse-proxy configuration (see [our nginx reverse-proxy doc page](configuring-playbook-nginx.md#synapse-openid-connect-for-single-sign-on)).
 
+This example configuration is for [keycloak](https://www.keycloak.org/), an opensource Identity Provider maintained by Red Hat.
+
+For more detailed documentation on available options and how to setup keycloak, see the [Synapse documentation on OpenID Connect with keycloak](https://github.com/matrix-org/synapse/blob/develop/docs/openid.md#keycloak).
+
 In case you encounter errors regarding the parsing of the variables, you can try to add `{% raw %}` and `{% endraw %}` blocks around them. For example ;
 
 ```
+matrix_synapse_configuration_extension_yaml: |
+  oidc_providers:
     - idp_id: keycloak
-        idp_name: "Keycloak"
-        issuer: "https://url.ix/auth/realms/x"
+      idp_name: "My KeyCloak server"
+      issuer: "https://url.ix/auth/realms/{realm_name}"
       client_id: "matrix"
       client_secret: "{{ vault_synapse_keycloak }}"
       scopes: ["openid", "profile"]
-        authorization_endpoint: "https://url.ix/auth/realms/x/protocol/openid-connect/auth"
-        token_endpoint: "https://url.ix/auth/realms/x/protocol/openid-connect/token"
-        userinfo_endpoint: "https://url.ix/auth/realms/x/protocol/openid-connect/userinfo"
       user_mapping_provider:
         config:
-            display_name_template: "{% raw %}{{ user.given_name }}{% endraw %} {% raw %}{{ user.family_name }}{% endraw %}"
+          localpart_template: "{% raw %}{{ user.preferred_username }}{% endraw %}"
+          display_name_template: "{% raw %}{{ user.name }}{% endraw %}"
           email_template: "{% raw %}{{ user.email }}{% endraw %}"
+      allow_existing_users: true # Optional
+      backchannel_logout_enabled: true # Optional
 ```