diff --git a/.env.example b/.env.example
index 5337042..c0205d9 100644
--- a/.env.example
+++ b/.env.example
@@ -49,7 +49,12 @@ KNOWLEDGE_CACHE_TTL=300
 # ======================
 # Authentication (Authentik OIDC)
 # ======================
-# Authentik Server URLs
+# Set to 'true' to enable OIDC authentication with Authentik
+# When enabled, OIDC_ISSUER, OIDC_CLIENT_ID, and OIDC_CLIENT_SECRET are required
+OIDC_ENABLED=false
+
+# Authentik Server URLs (required when OIDC_ENABLED=true)
+# OIDC_ISSUER must end with a trailing slash (/)
 OIDC_ISSUER=https://auth.example.com/application/o/mosaic-stack/
 OIDC_CLIENT_ID=your-client-id-here
 OIDC_CLIENT_SECRET=your-client-secret-here
diff --git a/apps/api/src/auth/auth.config.spec.ts b/apps/api/src/auth/auth.config.spec.ts
new file mode 100644
index 0000000..cdf422c
--- /dev/null
+++ b/apps/api/src/auth/auth.config.spec.ts
@@ -0,0 +1,138 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+import { isOidcEnabled, validateOidcConfig } from "./auth.config";
+
+describe("auth.config", () => {
+  // Store original env vars to restore after each test
+  const originalEnv = { ...process.env };
+
+  beforeEach(() => {
+    // Clear relevant env vars before each test
+    delete process.env.OIDC_ENABLED;
+    delete process.env.OIDC_ISSUER;
+    delete process.env.OIDC_CLIENT_ID;
+    delete process.env.OIDC_CLIENT_SECRET;
+  });
+
+  afterEach(() => {
+    // Restore original env vars
+    process.env = { ...originalEnv };
+  });
+
+  describe("isOidcEnabled", () => {
+    it("should return false when OIDC_ENABLED is not set", () => {
+      expect(isOidcEnabled()).toBe(false);
+    });
+
+    it("should return false when OIDC_ENABLED is 'false'", () => {
+      process.env.OIDC_ENABLED = "false";
+      expect(isOidcEnabled()).toBe(false);
+    });
+
+    it("should return false when OIDC_ENABLED is '0'", () => {
+      process.env.OIDC_ENABLED = "0";
+      expect(isOidcEnabled()).toBe(false);
+    });
+
+    it("should return false when OIDC_ENABLED is empty string", () => {
+      process.env.OIDC_ENABLED = "";
+      expect(isOidcEnabled()).toBe(false);
+    });
+
+    it("should return true when OIDC_ENABLED is 'true'", () => {
+      process.env.OIDC_ENABLED = "true";
+      expect(isOidcEnabled()).toBe(true);
+    });
+
+    it("should return true when OIDC_ENABLED is '1'", () => {
+      process.env.OIDC_ENABLED = "1";
+      expect(isOidcEnabled()).toBe(true);
+    });
+  });
+
+  describe("validateOidcConfig", () => {
+    describe("when OIDC is disabled", () => {
+      it("should not throw when OIDC_ENABLED is not set", () => {
+        expect(() => validateOidcConfig()).not.toThrow();
+      });
+
+      it("should not throw when OIDC_ENABLED is false even if vars are missing", () => {
+        process.env.OIDC_ENABLED = "false";
+        // Intentionally not setting any OIDC vars
+        expect(() => validateOidcConfig()).not.toThrow();
+      });
+    });
+
+    describe("when OIDC is enabled", () => {
+      beforeEach(() => {
+        process.env.OIDC_ENABLED = "true";
+      });
+
+      it("should throw when OIDC_ISSUER is missing", () => {
+        process.env.OIDC_CLIENT_ID = "test-client-id";
+        process.env.OIDC_CLIENT_SECRET = "test-client-secret";
+
+        expect(() => validateOidcConfig()).toThrow("OIDC_ISSUER");
+        expect(() => validateOidcConfig()).toThrow("OIDC authentication is enabled");
+      });
+
+      it("should throw when OIDC_CLIENT_ID is missing", () => {
+        process.env.OIDC_ISSUER = "https://auth.example.com/";
+        process.env.OIDC_CLIENT_SECRET = "test-client-secret";
+
+        expect(() => validateOidcConfig()).toThrow("OIDC_CLIENT_ID");
+      });
+
+      it("should throw when OIDC_CLIENT_SECRET is missing", () => {
+        process.env.OIDC_ISSUER = "https://auth.example.com/";
+        process.env.OIDC_CLIENT_ID = "test-client-id";
+
+        expect(() => validateOidcConfig()).toThrow("OIDC_CLIENT_SECRET");
+      });
+
+      it("should throw when all required vars are missing", () => {
+        expect(() => validateOidcConfig()).toThrow(
+          "OIDC_ISSUER, OIDC_CLIENT_ID, OIDC_CLIENT_SECRET"
+        );
+      });
+
+      it("should throw when vars are empty strings", () => {
+        process.env.OIDC_ISSUER = "";
+        process.env.OIDC_CLIENT_ID = "";
+        process.env.OIDC_CLIENT_SECRET = "";
+
+        expect(() => validateOidcConfig()).toThrow(
+          "OIDC_ISSUER, OIDC_CLIENT_ID, OIDC_CLIENT_SECRET"
+        );
+      });
+
+      it("should throw when vars are whitespace only", () => {
+        process.env.OIDC_ISSUER = "   ";
+        process.env.OIDC_CLIENT_ID = "test-client-id";
+        process.env.OIDC_CLIENT_SECRET = "test-client-secret";
+
+        expect(() => validateOidcConfig()).toThrow("OIDC_ISSUER");
+      });
+
+      it("should throw when OIDC_ISSUER does not end with trailing slash", () => {
+        process.env.OIDC_ISSUER = "https://auth.example.com/application/o/mosaic";
+        process.env.OIDC_CLIENT_ID = "test-client-id";
+        process.env.OIDC_CLIENT_SECRET = "test-client-secret";
+
+        expect(() => validateOidcConfig()).toThrow("OIDC_ISSUER must end with a trailing slash");
+        expect(() => validateOidcConfig()).toThrow("https://auth.example.com/application/o/mosaic");
+      });
+
+      it("should not throw with valid complete configuration", () => {
+        process.env.OIDC_ISSUER = "https://auth.example.com/application/o/mosaic-stack/";
+        process.env.OIDC_CLIENT_ID = "test-client-id";
+        process.env.OIDC_CLIENT_SECRET = "test-client-secret";
+
+        expect(() => validateOidcConfig()).not.toThrow();
+      });
+
+      it("should suggest disabling OIDC in error message", () => {
+        expect(() => validateOidcConfig()).toThrow("OIDC_ENABLED=false");
+      });
+    });
+  });
+});
diff --git a/apps/api/src/auth/auth.config.ts b/apps/api/src/auth/auth.config.ts
index 8abefed..e07b2e4 100644
--- a/apps/api/src/auth/auth.config.ts
+++ b/apps/api/src/auth/auth.config.ts
@@ -3,7 +3,85 @@ import { prismaAdapter } from "better-auth/adapters/prisma";
 import { genericOAuth } from "better-auth/plugins";
 import type { PrismaClient } from "@prisma/client";
 
+/**
+ * Required OIDC environment variables when OIDC is enabled
+ */
+const REQUIRED_OIDC_ENV_VARS = ["OIDC_ISSUER", "OIDC_CLIENT_ID", "OIDC_CLIENT_SECRET"] as const;
+
+/**
+ * Check if OIDC authentication is enabled via environment variable
+ */
+export function isOidcEnabled(): boolean {
+  const enabled = process.env.OIDC_ENABLED;
+  return enabled === "true" || enabled === "1";
+}
+
+/**
+ * Validates OIDC configuration at startup.
+ * Throws an error if OIDC is enabled but required environment variables are missing.
+ *
+ * @throws Error if OIDC is enabled but required vars are missing or empty
+ */
+export function validateOidcConfig(): void {
+  if (!isOidcEnabled()) {
+    // OIDC is disabled, no validation needed
+    return;
+  }
+
+  const missingVars: string[] = [];
+
+  for (const envVar of REQUIRED_OIDC_ENV_VARS) {
+    const value = process.env[envVar];
+    if (!value || value.trim() === "") {
+      missingVars.push(envVar);
+    }
+  }
+
+  if (missingVars.length > 0) {
+    throw new Error(
+      `OIDC authentication is enabled (OIDC_ENABLED=true) but required environment variables are missing or empty: ${missingVars.join(", ")}. ` +
+        `Either set these variables or disable OIDC by setting OIDC_ENABLED=false.`
+    );
+  }
+
+  // Additional validation: OIDC_ISSUER should end with a trailing slash for proper discovery URL
+  const issuer = process.env.OIDC_ISSUER;
+  if (issuer && !issuer.endsWith("/")) {
+    throw new Error(
+      `OIDC_ISSUER must end with a trailing slash (/). Current value: "${issuer}". ` +
+        `The discovery URL is constructed by appending ".well-known/openid-configuration" to the issuer.`
+    );
+  }
+}
+
+/**
+ * Get OIDC plugins configuration.
+ * Returns empty array if OIDC is disabled, otherwise returns configured OAuth plugin.
+ */
+function getOidcPlugins(): ReturnType<typeof genericOAuth>[] {
+  if (!isOidcEnabled()) {
+    return [];
+  }
+
+  return [
+    genericOAuth({
+      config: [
+        {
+          providerId: "authentik",
+          clientId: process.env.OIDC_CLIENT_ID ?? "",
+          clientSecret: process.env.OIDC_CLIENT_SECRET ?? "",
+          discoveryUrl: `${process.env.OIDC_ISSUER ?? ""}.well-known/openid-configuration`,
+          scopes: ["openid", "profile", "email"],
+        },
+      ],
+    }),
+  ];
+}
+
 export function createAuth(prisma: PrismaClient) {
+  // Validate OIDC configuration at startup - fail fast if misconfigured
+  validateOidcConfig();
+
   return betterAuth({
     database: prismaAdapter(prisma, {
       provider: "postgresql",
@@ -11,19 +89,7 @@ export function createAuth(prisma: PrismaClient) {
     emailAndPassword: {
       enabled: true, // Enable for now, can be disabled later
     },
-    plugins: [
-      genericOAuth({
-        config: [
-          {
-            providerId: "authentik",
-            clientId: process.env.OIDC_CLIENT_ID ?? "",
-            clientSecret: process.env.OIDC_CLIENT_SECRET ?? "",
-            discoveryUrl: `${process.env.OIDC_ISSUER ?? ""}.well-known/openid-configuration`,
-            scopes: ["openid", "profile", "email"],
-          },
-        ],
-      }),
-    ],
+    plugins: [...getOidcPlugins()],
     session: {
       expiresIn: 60 * 60 * 24, // 24 hours
       updateAge: 60 * 60 * 24, // 24 hours