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src/metrics/metrics.module.ts

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+import { Module } from '@nestjs/common';
+import {
+  PrometheusModule,
+  makeCounterProvider,
+  makeGaugeProvider,
+} from '@willsoto/nestjs-prometheus';
+import { MetricsService } from './metrics.service';
+
+@Module({
+  imports: [
+    PrometheusModule.register({
+      path: '/metrics',
+      defaultMetrics: { enabled: true },
+    }),
+  ],
+  providers: [
+    MetricsService,
+    makeCounterProvider({
+      name: 'sso_logins_total',
+      help: 'Total number of successful logins',
+    }),
+    makeCounterProvider({
+      name: 'sso_logins_failed_total',
+      help: 'Total number of failed login attempts',
+    }),
+    makeGaugeProvider({
+      name: 'sso_active_sessions',
+      help: 'Number of active sessions',
+    }),
+  ],
+  exports: [MetricsService],
+})
+export class MetricsModule {}

src/metrics/metrics.service.ts

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+import { Injectable } from '@nestjs/common';
+import { InjectMetric } from '@willsoto/nestjs-prometheus';
+import { Counter, Gauge } from 'prom-client';
+
+@Injectable()
+export class MetricsService {
+  constructor(
+    @InjectMetric('sso_logins_total')
+    private readonly loginsCounter: Counter<string>,
+    @InjectMetric('sso_logins_failed_total')
+    private readonly failedLoginsCounter: Counter<string>,
+    @InjectMetric('sso_active_sessions')
+    private readonly activeSessionsGauge: Gauge<string>,
+  ) {}
+
+  incrementLogins(): void {
+    this.loginsCounter.inc();
+  }
+
+  incrementFailedLogins(): void {
+    this.failedLoginsCounter.inc();
+  }
+
+  setActiveSessions(count: number): void {
+    this.activeSessionsGauge.set(count);
+  }
+}