Add new unique constraint and improved nonce-checking logic

database/migrations/2026_05_05_125206_add_unique_index_to_nonces.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('saml_nonces', function (Blueprint $table) {
+            $table->dropIndex(['nonce']);
+            $table->unique('nonce');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('saml_nonces', function (Blueprint $table) {
+            $table->dropUnique(['nonce']);
+            $table->index('nonce');
+        });
+    }
+};