feat(#413): add OIDC provider health check with 30s cache

- isOidcProviderReachable() fetches discovery URL with 2s timeout
- getAuthConfig() omits authentik when provider unreachable
- 30-second cache prevents repeated network calls

Refs #413

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/auth/auth.service.spec.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, beforeEach, vi } from "vitest";
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 import { Test, TestingModule } from "@nestjs/testing";
 import { AuthService } from "./auth.service";
 import { PrismaService } from "../prisma/prisma.service";
@@ -30,6 +30,12 @@ describe("AuthService", () => {
     vi.clearAllMocks();
   });
 
+  afterEach(() => {
+    vi.restoreAllMocks();
+    delete process.env.OIDC_ENABLED;
+    delete process.env.OIDC_ISSUER;
+  });
+
   describe("getAuth", () => {
     it("should return BetterAuth instance", () => {
       const auth = service.getAuth();
@@ -90,21 +96,128 @@ describe("AuthService", () => {
     });
   });
 
+  describe("isOidcProviderReachable", () => {
+    const discoveryUrl = "https://auth.example.com/.well-known/openid-configuration";
+
+    beforeEach(() => {
+      process.env.OIDC_ISSUER = "https://auth.example.com/";
+      // Reset the cache by accessing private fields via bracket notation
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      (service as any).lastHealthCheck = 0;
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      (service as any).lastHealthResult = false;
+    });
+
+    it("should return true when discovery URL returns 200", async () => {
+      const mockFetch = vi.fn().mockResolvedValue({
+        ok: true,
+        status: 200,
+      });
+      vi.stubGlobal("fetch", mockFetch);
+
+      const result = await service.isOidcProviderReachable();
+
+      expect(result).toBe(true);
+      expect(mockFetch).toHaveBeenCalledWith(discoveryUrl, {
+        signal: expect.any(AbortSignal) as AbortSignal,
+      });
+    });
+
+    it("should return false on network error", async () => {
+      const mockFetch = vi.fn().mockRejectedValue(new Error("ECONNREFUSED"));
+      vi.stubGlobal("fetch", mockFetch);
+
+      const result = await service.isOidcProviderReachable();
+
+      expect(result).toBe(false);
+    });
+
+    it("should return false on timeout", async () => {
+      const mockFetch = vi.fn().mockRejectedValue(new DOMException("The operation was aborted"));
+      vi.stubGlobal("fetch", mockFetch);
+
+      const result = await service.isOidcProviderReachable();
+
+      expect(result).toBe(false);
+    });
+
+    it("should return false when discovery URL returns non-200", async () => {
+      const mockFetch = vi.fn().mockResolvedValue({
+        ok: false,
+        status: 503,
+      });
+      vi.stubGlobal("fetch", mockFetch);
+
+      const result = await service.isOidcProviderReachable();
+
+      expect(result).toBe(false);
+    });
+
+    it("should cache result for 30 seconds", async () => {
+      const mockFetch = vi.fn().mockResolvedValue({
+        ok: true,
+        status: 200,
+      });
+      vi.stubGlobal("fetch", mockFetch);
+
+      // First call - fetches
+      const result1 = await service.isOidcProviderReachable();
+      expect(result1).toBe(true);
+      expect(mockFetch).toHaveBeenCalledTimes(1);
+
+      // Second call within 30s - uses cache
+      const result2 = await service.isOidcProviderReachable();
+      expect(result2).toBe(true);
+      expect(mockFetch).toHaveBeenCalledTimes(1); // Still 1, no new fetch
+
+      // Simulate cache expiry by moving lastHealthCheck back
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      (service as any).lastHealthCheck = Date.now() - 31_000;
+
+      // Third call after cache expiry - fetches again
+      const result3 = await service.isOidcProviderReachable();
+      expect(result3).toBe(true);
+      expect(mockFetch).toHaveBeenCalledTimes(2); // Now 2
+    });
+
+    it("should cache false results too", async () => {
+      const mockFetch = vi
+        .fn()
+        .mockRejectedValueOnce(new Error("ECONNREFUSED"))
+        .mockResolvedValueOnce({ ok: true, status: 200 });
+      vi.stubGlobal("fetch", mockFetch);
+
+      // First call - fails
+      const result1 = await service.isOidcProviderReachable();
+      expect(result1).toBe(false);
+      expect(mockFetch).toHaveBeenCalledTimes(1);
+
+      // Second call within 30s - returns cached false
+      const result2 = await service.isOidcProviderReachable();
+      expect(result2).toBe(false);
+      expect(mockFetch).toHaveBeenCalledTimes(1);
+    });
+  });
+
   describe("getAuthConfig", () => {
-    it("should return only email provider when OIDC is disabled", () => {
+    it("should return only email provider when OIDC is disabled", async () => {
       delete process.env.OIDC_ENABLED;
 
-      const result = service.getAuthConfig();
+      const result = await service.getAuthConfig();
 
       expect(result).toEqual({
         providers: [{ id: "email", name: "Email", type: "credentials" }],
       });
     });
 
-    it("should return both email and authentik providers when OIDC is enabled", () => {
+    it("should return both email and authentik providers when OIDC is enabled and reachable", async () => {
       process.env.OIDC_ENABLED = "true";
+      process.env.OIDC_ISSUER = "https://auth.example.com/";
 
-      const result = service.getAuthConfig();
+      const mockFetch = vi.fn().mockResolvedValue({ ok: true, status: 200 });
+      vi.stubGlobal("fetch", mockFetch);
+
+      const result = await service.getAuthConfig();
 
       expect(result).toEqual({
         providers: [
@@ -112,20 +225,34 @@ describe("AuthService", () => {
           { id: "authentik", name: "Authentik", type: "oauth" },
         ],
       });
-
-      delete process.env.OIDC_ENABLED;
     });
 
-    it("should return only email provider when OIDC_ENABLED is false", () => {
+    it("should return only email provider when OIDC_ENABLED is false", async () => {
       process.env.OIDC_ENABLED = "false";
 
-      const result = service.getAuthConfig();
+      const result = await service.getAuthConfig();
 
       expect(result).toEqual({
         providers: [{ id: "email", name: "Email", type: "credentials" }],
       });
+    });
 
-      delete process.env.OIDC_ENABLED;
+    it("should omit authentik when OIDC is enabled but provider is unreachable", async () => {
+      process.env.OIDC_ENABLED = "true";
+      process.env.OIDC_ISSUER = "https://auth.example.com/";
+
+      // Reset cache
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      (service as any).lastHealthCheck = 0;
+
+      const mockFetch = vi.fn().mockRejectedValue(new Error("ECONNREFUSED"));
+      vi.stubGlobal("fetch", mockFetch);
+
+      const result = await service.getAuthConfig();
+
+      expect(result).toEqual({
+        providers: [{ id: "email", name: "Email", type: "credentials" }],
+      });
     });
   });