Support OIDC backchannel logouts (#11414)

If configured an OIDC IdP can log a user's session out of
Synapse when they log out of the identity provider.

The IdP sends a request directly to Synapse (and must be
configured with an endpoint) when a user logs out.

1 files changed, 9 insertions, 0 deletions

diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md

index 97fb505a5f..44358faf59 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -3021,6 +3021,15 @@ Options for each entry include:
      which is set to the claims returned by the UserInfo Endpoint and/or
      in the ID Token.
 
+* `backchannel_logout_enabled`: set to `true` to process OIDC Back-Channel Logout notifications. 
+  Those notifications are expected to be received on `/_synapse/client/oidc/backchannel_logout`.
+  Defaults to `false`.
+
+* `backchannel_logout_ignore_sub`: by default, the OIDC Back-Channel Logout feature checks that the
+  `sub` claim matches the subject claim received during login. This check can be disabled by setting
+  this to `true`. Defaults to `false`.
+
+  You might want to disable this if the `subject_claim` returned by the mapping provider is not `sub`.
 
 It is possible to configure Synapse to only allow logins if certain attributes
 match particular values in the OIDC userinfo. The requirements can be listed under