diff --git a/CHANGELOG.md b/CHANGELOG.md
index ca0d05c14..8f44c21fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgraded `papaparse` from version `5.5.3` to `5.7.0`
 - Upgraded `zone.js` from version `0.16.2` to `0.16.3`
 
+### Fixed
+
+- Hardened the authentication with _OpenID Connect_ (`OIDC`) (experimental)
+
 ## 3.69.0 - 2026-09-07
 
 ### Changed
diff --git a/apps/api/src/app/auth/oidc-state.store.ts b/apps/api/src/app/auth/oidc-state.store.ts
index aebd99892..0131d184d 100644
--- a/apps/api/src/app/auth/oidc-state.store.ts
+++ b/apps/api/src/app/auth/oidc-state.store.ts
@@ -1,5 +1,6 @@
 import type { Request } from 'express';
 import ms from 'ms';
+import { randomBytes } from 'node:crypto';
 import type {
   SessionStore,
   SessionStoreCallback,
@@ -66,13 +67,20 @@ export class OidcStateStore implements SessionStore {
       const data = this.stateMap.get(handle);
 
       if (!data) {
-        return callback(null, undefined, undefined);
+        return callback(
+          new Error('Invalid OIDC state parameter'),
+          undefined,
+          undefined
+        );
       }
 
       if (Date.now() - data.timestamp > this.STATE_EXPIRY_MS) {
-        // State has expired
         this.stateMap.delete(handle);
-        return callback(null, undefined, undefined);
+        return callback(
+          new Error('OIDC state has expired, please try again'),
+          undefined,
+          undefined
+        );
       }
 
       // Remove state after verification (one-time use)
@@ -106,10 +114,6 @@ export class OidcStateStore implements SessionStore {
    * Generate a cryptographically secure random handle
    */
   private generateHandle() {
-    return (
-      Math.random().toString(36).substring(2, 15) +
-      Math.random().toString(36).substring(2, 15) +
-      Date.now().toString(36)
-    );
+    return randomBytes(32).toString('hex');
   }
 }
diff --git a/apps/api/src/guards/oauth-callback.guard.ts b/apps/api/src/guards/oauth-callback.guard.ts
index cedbccde1..a89d77daa 100644
--- a/apps/api/src/guards/oauth-callback.guard.ts
+++ b/apps/api/src/guards/oauth-callback.guard.ts
@@ -5,11 +5,19 @@ export function OAuthCallbackGuard(strategy: string): Type<IAuthGuard> {
   class OAuthCallbackGuardMixin extends AuthGuard(strategy) {
     private readonly logger = new Logger(OAuthCallbackGuard.name);
 
-    public override handleRequest(error: Error, user: any) {
+    public override handleRequest(
+      error: Error | null,
+      user: any,
+      info?: { message?: string }
+    ) {
       if (error) {
         this.logger.error(
           `Authentication with the ${strategy} strategy has failed: ${error.message}`
         );
+      } else if (!user && info?.message) {
+        this.logger.warn(
+          `Authentication with the ${strategy} strategy was rejected: ${info.message}`
+        );
       }
 
       // Do not throw, the callback handler redirects to the login page instead