Update configuring-playbook-synapse.md

Added an example for configuring the variables for the OpenID, that might fails because the variables are not defined for the playbook parsing, but Synapse's own config file parsing.

docs/configuring-playbook-synapse.md

@@ -55,3 +55,22 @@ Certain Synapse administration tasks (managing users and rooms, etc.) can be per
 ## Synapse + OpenID Connect for Single-Sign-On
 
 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)).
+
+In case you encounter errors regarding the parsing of the variables, you can try to add `{%raw}` and `{% endraw %}` blocks around them. For example ;
+
+```
+ - idp_id: keycloak
+        idp_name: "Keycloak"
+        issuer: "https://url.ix/auth/realms/x"
+        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 %}"
+            email_template: "{%raw}{{ user.email }}{% endraw %}"
+```
+