diff --git a/apps/api/src/auth/auth.config.spec.ts b/apps/api/src/auth/auth.config.spec.ts
index a05649f..05c7c99 100644
--- a/apps/api/src/auth/auth.config.spec.ts
+++ b/apps/api/src/auth/auth.config.spec.ts
@@ -35,6 +35,7 @@ describe("auth.config", () => {
     delete process.env.NEXT_PUBLIC_APP_URL;
     delete process.env.NEXT_PUBLIC_API_URL;
     delete process.env.TRUSTED_ORIGINS;
+    delete process.env.COOKIE_DOMAIN;
   });
 
   afterEach(() => {
@@ -185,6 +186,7 @@ describe("auth.config", () => {
 
           expect(() => validateOidcConfig()).toThrow("OIDC_REDIRECT_URI must be a valid URL");
           expect(() => validateOidcConfig()).toThrow("not-a-url");
+          expect(() => validateOidcConfig()).toThrow("Parse error:");
         });
 
         it("should throw when OIDC_REDIRECT_URI path does not start with /auth/callback", () => {
@@ -404,6 +406,40 @@ describe("auth.config", () => {
       expect(origins).toContain("http://localhost:3001");
       expect(origins).toHaveLength(5);
     });
+
+    it("should reject invalid URLs in TRUSTED_ORIGINS with a warning", () => {
+      process.env.TRUSTED_ORIGINS = "not-a-url,https://valid.example.com";
+      process.env.NODE_ENV = "production";
+
+      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+
+      const origins = getTrustedOrigins();
+
+      expect(origins).toContain("https://valid.example.com");
+      expect(origins).not.toContain("not-a-url");
+      expect(warnSpy).toHaveBeenCalledWith(
+        expect.stringContaining('Ignoring invalid URL in TRUSTED_ORIGINS: "not-a-url"')
+      );
+
+      warnSpy.mockRestore();
+    });
+
+    it("should reject non-HTTP origins in TRUSTED_ORIGINS with a warning", () => {
+      process.env.TRUSTED_ORIGINS = "ftp://files.example.com,https://valid.example.com";
+      process.env.NODE_ENV = "production";
+
+      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+
+      const origins = getTrustedOrigins();
+
+      expect(origins).toContain("https://valid.example.com");
+      expect(origins).not.toContain("ftp://files.example.com");
+      expect(warnSpy).toHaveBeenCalledWith(
+        expect.stringContaining("Ignoring non-HTTP origin in TRUSTED_ORIGINS")
+      );
+
+      warnSpy.mockRestore();
+    });
   });
 
   describe("createAuth - session and cookie configuration", () => {
@@ -504,5 +540,43 @@ describe("auth.config", () => {
       };
       expect(config.advanced.defaultCookieAttributes.secure).toBe(false);
     });
+
+    it("should set cookie domain when COOKIE_DOMAIN env var is present", () => {
+      process.env.COOKIE_DOMAIN = ".mosaicstack.dev";
+      const mockPrisma = {} as PrismaClient;
+      createAuth(mockPrisma);
+
+      expect(mockBetterAuth).toHaveBeenCalledOnce();
+      const config = mockBetterAuth.mock.calls[0][0] as {
+        advanced: {
+          defaultCookieAttributes: {
+            httpOnly: boolean;
+            secure: boolean;
+            sameSite: string;
+            domain?: string;
+          };
+        };
+      };
+      expect(config.advanced.defaultCookieAttributes.domain).toBe(".mosaicstack.dev");
+    });
+
+    it("should not set cookie domain when COOKIE_DOMAIN env var is absent", () => {
+      delete process.env.COOKIE_DOMAIN;
+      const mockPrisma = {} as PrismaClient;
+      createAuth(mockPrisma);
+
+      expect(mockBetterAuth).toHaveBeenCalledOnce();
+      const config = mockBetterAuth.mock.calls[0][0] as {
+        advanced: {
+          defaultCookieAttributes: {
+            httpOnly: boolean;
+            secure: boolean;
+            sameSite: string;
+            domain?: string;
+          };
+        };
+      };
+      expect(config.advanced.defaultCookieAttributes.domain).toBeUndefined();
+    });
   });
 });
diff --git a/apps/api/src/auth/auth.config.ts b/apps/api/src/auth/auth.config.ts
index 568f242..c97f2a1 100644
--- a/apps/api/src/auth/auth.config.ts
+++ b/apps/api/src/auth/auth.config.ts
@@ -80,9 +80,11 @@ function validateRedirectUri(): void {
   let parsed: URL;
   try {
     parsed = new URL(redirectUri);
-  } catch {
+  } catch (urlError: unknown) {
+    const detail = urlError instanceof Error ? urlError.message : String(urlError);
     throw new Error(
       `OIDC_REDIRECT_URI must be a valid URL. Current value: "${redirectUri}". ` +
+        `Parse error: ${detail}. ` +
         `Example: "https://app.example.com/auth/callback/authentik".`
     );
   }
@@ -153,12 +155,23 @@ export function getTrustedOrigins(): string[] {
     origins.push(process.env.NEXT_PUBLIC_API_URL);
   }
 
-  // Comma-separated additional origins
+  // Comma-separated additional origins (validated)
   if (process.env.TRUSTED_ORIGINS) {
-    const extra = process.env.TRUSTED_ORIGINS.split(",")
+    const rawOrigins = process.env.TRUSTED_ORIGINS.split(",")
       .map((o) => o.trim())
       .filter((o) => o !== "");
-    origins.push(...extra);
+    for (const origin of rawOrigins) {
+      try {
+        const parsed = new URL(origin);
+        if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
+          console.warn(`[AUTH] Ignoring non-HTTP origin in TRUSTED_ORIGINS: "${origin}"`);
+          continue;
+        }
+        origins.push(origin);
+      } catch {
+        console.warn(`[AUTH] Ignoring invalid URL in TRUSTED_ORIGINS: "${origin}"`);
+      }
+    }
   }
 
   // Localhost fallbacks for development only
@@ -192,6 +205,7 @@ export function createAuth(prisma: PrismaClient) {
         httpOnly: true,
         secure: process.env.NODE_ENV === "production",
         sameSite: "lax" as const,
+        ...(process.env.COOKIE_DOMAIN ? { domain: process.env.COOKIE_DOMAIN } : {}),
       },
     },
     trustedOrigins: getTrustedOrigins(),
diff --git a/apps/api/src/auth/auth.service.spec.ts b/apps/api/src/auth/auth.service.spec.ts
index 3e464c4..508fa10 100644
--- a/apps/api/src/auth/auth.service.spec.ts
+++ b/apps/api/src/auth/auth.service.spec.ts
@@ -1,5 +1,26 @@
 import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 import { Test, TestingModule } from "@nestjs/testing";
+
+// Mock better-auth modules before importing AuthService
+vi.mock("better-auth/node", () => ({
+  toNodeHandler: vi.fn().mockReturnValue(vi.fn()),
+}));
+
+vi.mock("better-auth", () => ({
+  betterAuth: vi.fn().mockReturnValue({
+    handler: vi.fn(),
+    api: { getSession: vi.fn() },
+  }),
+}));
+
+vi.mock("better-auth/adapters/prisma", () => ({
+  prismaAdapter: vi.fn().mockReturnValue({}),
+}));
+
+vi.mock("better-auth/plugins", () => ({
+  genericOAuth: vi.fn().mockReturnValue({ id: "generic-oauth" }),
+}));
+
 import { AuthService } from "./auth.service";
 import { PrismaService } from "../prisma/prisma.service";
 
@@ -294,7 +315,7 @@ describe("AuthService", () => {
       expect(result).toBeNull();
     });
 
-    it("should return null and log error on verification failure", async () => {
+    it("should return null and log warning on auth verification failure", async () => {
       const auth = service.getAuth();
       const mockGetSession = vi.fn().mockRejectedValue(new Error("Verification failed"));
       auth.api = { getSession: mockGetSession } as any;
@@ -303,5 +324,38 @@ describe("AuthService", () => {
 
       expect(result).toBeNull();
     });
+
+    it("should re-throw Prisma infrastructure errors", async () => {
+      const auth = service.getAuth();
+      const prismaError = new Error("connect ECONNREFUSED 127.0.0.1:5432");
+      const mockGetSession = vi.fn().mockRejectedValue(prismaError);
+      auth.api = { getSession: mockGetSession } as any;
+
+      await expect(service.verifySession("any-token")).rejects.toThrow("ECONNREFUSED");
+    });
+
+    it("should re-throw timeout errors as infrastructure errors", async () => {
+      const auth = service.getAuth();
+      const timeoutError = new Error("Connection timeout after 5000ms");
+      const mockGetSession = vi.fn().mockRejectedValue(timeoutError);
+      auth.api = { getSession: mockGetSession } as any;
+
+      await expect(service.verifySession("any-token")).rejects.toThrow("timeout");
+    });
+
+    it("should re-throw errors with Prisma-prefixed constructor name", async () => {
+      const auth = service.getAuth();
+      class PrismaClientKnownRequestError extends Error {
+        constructor(message: string) {
+          super(message);
+          this.name = "PrismaClientKnownRequestError";
+        }
+      }
+      const prismaError = new PrismaClientKnownRequestError("Database connection lost");
+      const mockGetSession = vi.fn().mockRejectedValue(prismaError);
+      auth.api = { getSession: mockGetSession } as any;
+
+      await expect(service.verifySession("any-token")).rejects.toThrow("Database connection lost");
+    });
   });
 });
diff --git a/apps/api/src/auth/auth.service.ts b/apps/api/src/auth/auth.service.ts
index 13559df..4bfd489 100644
--- a/apps/api/src/auth/auth.service.ts
+++ b/apps/api/src/auth/auth.service.ts
@@ -108,9 +108,26 @@ export class AuthService {
         session: session.session as Record<string, unknown>,
       };
     } catch (error) {
-      this.logger.error(
+      // Infrastructure errors (database down, connection failures) should propagate
+      // so the global exception filter returns 500/503, not 401
+      if (
+        error instanceof Error &&
+        (error.constructor.name.startsWith("Prisma") ||
+          error.message.includes("connect") ||
+          error.message.includes("ECONNREFUSED") ||
+          error.message.includes("timeout"))
+      ) {
+        this.logger.error(
+          "Session verification failed due to infrastructure error",
+          error.stack,
+        );
+        throw error;
+      }
+
+      // Expected auth errors (invalid/expired token) return null
+      this.logger.warn(
         "Session verification failed",
-        error instanceof Error ? error.message : "Unknown error"
+        error instanceof Error ? error.message : "Unknown error",
       );
       return null;
     }