8000 Reject a different brokered user on forced re-authentication before c… by sguilhen · Pull Request #54462 · keycloak/keycloak · GitHub
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Reject a different brokered user on forced re-authentication before c… #54462

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Merged
pedroigor merged 1 commit into from
Nov 6, 2026
Merged

Reject a different brokered user on forced re-authentication before c… #54462

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22 changes: 22 additions & 0 deletions ...org/keycloak/authentication/authenticators/broker/IdpCreateUserIfUniqueAuthenticator.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,8 +35,11 @@
import org.keycloak.models.RealmModel;
import org.keycloak.models.UserModel;
import org.keycloak.models.UserProvider;
import org.keycloak.models.UserSessionModel;
import org.keycloak.models.light.LightweightUserAdapter;
import org.keycloak.services.ErrorPageException;
import org.keycloak.services.ServicesLogger;
import org.keycloak.services.managers.AuthenticationManager;
import org.keycloak.services.messages.Messages;
import org.keycloak.userprofile.UserProfile;
import org.keycloak.userprofile.UserProfileContext;
Expand Down Expand Up @@ -97,6 +100,11 @@ protected void authenticateImpl(AuthenticationFlowContext context, SerializedBro
federatedUser = new LightweightUserAdapter(session, context.getAuthenticationSession().getParentSession().getId());
federatedUser.setUsername(username);
} else if (duplication == null) {
// A user that does not exist yet can never be the user of a session that is still valid (eg. on prompt=login).
// AuthenticationProcessor.attachSession() rejects that mismatch too, but only after the new user was committed
// without its identity link, which locks them out. Reject before creating it instead.
rejectIfAnotherUserHoldsTheSession(context);

logger.debugf("No duplication detected. Creating account for user '%s' and linking with identity provider '%s' .",
username, broker.getAlias());

Expand Down Expand Up @@ -161,6 +169,20 @@ protected void authenticateImpl(AuthenticationFlowContext context, SerializedBro
}
}

private void rejectIfAnotherUserHoldsTheSession(AuthenticationFlowContext context) {
KeycloakSession session = context.getSession();
RealmModel realm = context.getRealm();
// The authentication session shares its ID with the user session it was started on top of when the browser holds an SSO session.
UserSessionModel userSession = session.sessions().getUserSession(realm, context.getAuthenticationSession().getParentSession().getId());
if (userSession == null || userSession.getUser() == null || !AuthenticationManager.isSessionValid(realm, userSession)) {
return;
}

context.getEvent().detail(Details.EXISTING_USER, userSession.getUser().getId()).error(Errors.DIFFERENT_USER_AUTHENTICATED);
throw new ErrorPageException(session, context.getAuthenticationSession(), Response.Status.BAD_REQUEST,
Messages.DIFFERENT_USER_AUTHENTICATED, userSession.getUser().getUsername());
}

// Could be overriden to detect duplication based on other criterias (firstName, lastName, ...)
protected ExistingUserInfo checkExistingUser(AuthenticationFlowContext context, String username, SerializedBrokeredIdentityContext serializedCtx, BrokeredIdentityContext brokerContext) {

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