fix(login): CSP img-src resolved at build time instead of runtime (#11603)

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# Which Problems Are Solved

- On self-hosted ZITADEL, the CSP `img-src` directive was baked in at
build time from `ZITADEL_API_URL`, blocking branding logos when the
runtime domain differs from the build environment
- CSP construction was duplicated across three files with no single
source of truth

# How the Problems Are Solved

- Introduced a centralized `buildCSP()` function in `src/lib/csp.ts`
that constructs the full CSP string from runtime inputs (`serviceUrl`
for img-src, `iframeOrigins` for frame-ancestors)
- Middleware and flow-initiation now call `buildCSP()` instead of
concatenating strings against a static `DEFAULT_CSP`
- `constants/csp.js` is simplified to a static fallback used only by
`next.config.mjs`

# Additional Changes

- Removed no-op `securitySettings.embeddedIframe.allowedOrigins;`
statements in flow-initiation
- Removed duplicate `X-Frame-Options: SAMEORIGIN` header from
`next.config.mjs` (conflicted with `X-Frame-Options: deny`)
- Added `X-Frame-Options: deny` explicitly on proxy route responses in
middleware (previously relied on next.config.mjs static header surviving
the rewrite)

# Additional Context

- Closes #11088 
- Closes #11602

apps/login/constants/csp.js

@@ -1,6 +1,2 @@
-const ZITADEL_DOMAIN = process.env.ZITADEL_API_URL
-  ? new URL(process.env.ZITADEL_API_URL).hostname
-  : '*.zitadel.cloud';
-
 export const DEFAULT_CSP =
-  `default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; connect-src 'self'; child-src; style-src 'self' 'unsafe-inline'; font-src 'self'; object-src 'none'; img-src 'self' https://${ZITADEL_DOMAIN};`;
+  "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; connect-src 'self'; style-src 'self' 'unsafe-inline'; font-src 'self'; img-src 'self'; frame-ancestors 'none'; object-src 'none'";

apps/login/next.config.mjs

@@ -12,10 +12,6 @@ const secureHeaders = [
     key: "Referrer-Policy",
     value: "origin-when-cross-origin",
   },
-  {
-    key: "X-Frame-Options",
-    value: "SAMEORIGIN",
-  },
   {
     key: "X-Content-Type-Options",
     value: "nosniff",
@@ -26,7 +22,7 @@ const secureHeaders = [
   },
   {
     key: "Content-Security-Policy",
-    value: `${DEFAULT_CSP} frame-ancestors 'none'`,
+    value: DEFAULT_CSP,
   },
   { key: "X-Frame-Options", value: "deny" },
 ];

apps/login/src/lib/csp.test.ts

@@ -0,0 +1,63 @@
+import { describe, expect, test } from "vitest";
+import { buildCSP } from "./csp";
+
+describe("buildCSP", () => {
+  test("returns all base directives with safe defaults", () => {
+    const csp = buildCSP();
+
+    expect(csp).toContain("default-src 'self'");
+    expect(csp).toContain("script-src 'self' 'unsafe-inline' 'unsafe-eval'");
+    expect(csp).toContain("connect-src 'self'");
+    expect(csp).toContain("style-src 'self' 'unsafe-inline'");
+    expect(csp).toContain("font-src 'self'");
+    expect(csp).toContain("img-src 'self'");
+    expect(csp).toContain("object-src 'none'");
+    expect(csp).toContain("frame-ancestors 'none'");
+  });
+
+  test("adds serviceUrl to img-src only", () => {
+    const csp = buildCSP({ serviceUrl: "https://my-instance.zitadel.cloud" });
+
+    expect(csp).toContain("img-src 'self' https://my-instance.zitadel.cloud");
+    expect(csp).toMatch(/font-src 'self'(?:;| |$)/);
+  });
+
+  test("keeps frame-ancestors as 'none' when iframeOrigins is empty", () => {
+    const csp = buildCSP({ iframeOrigins: [] });
+
+    expect(csp).toContain("frame-ancestors 'none'");
+  });
+
+  test("overrides frame-ancestors when iframeOrigins are provided", () => {
+    const csp = buildCSP({
+      iframeOrigins: ["https://app.example.com", "https://other.example.com"],
+    });
+
+    expect(csp).toContain("frame-ancestors https://app.example.com https://other.example.com");
+    expect(csp).not.toContain("frame-ancestors 'none'");
+  });
+
+  test("combines serviceUrl and iframeOrigins", () => {
+    const csp = buildCSP({
+      serviceUrl: "https://zitadel.mycompany.com",
+      iframeOrigins: ["https://portal.mycompany.com"],
+    });
+
+    expect(csp).toContain("img-src 'self' https://zitadel.mycompany.com");
+    expect(csp).toContain("frame-ancestors https://portal.mycompany.com");
+    expect(csp).not.toContain("frame-ancestors 'none'");
+  });
+
+  test("base directives are preserved when options are set", () => {
+    const csp = buildCSP({
+      serviceUrl: "https://example.com",
+      iframeOrigins: ["https://embed.example.com"],
+    });
+
+    expect(csp).toContain("default-src 'self'");
+    expect(csp).toContain("script-src 'self' 'unsafe-inline' 'unsafe-eval'");
+    expect(csp).toContain("connect-src 'self'");
+    expect(csp).toContain("style-src 'self' 'unsafe-inline'");
+    expect(csp).toContain("object-src 'none'");
+  });
+});

apps/login/src/lib/csp.ts

@@ -0,0 +1,36 @@
+
+const BASE_DIRECTIVES: Record<string, string[]> = {
+  "default-src": ["'self'"],
+  "script-src": ["'self'", "'unsafe-inline'", "'unsafe-eval'"],
+  "connect-src": ["'self'"],
+  "style-src": ["'self'", "'unsafe-inline'"],
+  "font-src": ["'self'"],
+  "img-src": ["'self'"],
+  "frame-ancestors": ["'none'"],
+  "object-src": ["'none'"],
+};
+
+export interface CSPOptions {
+  serviceUrl?: string;
+  iframeOrigins?: string[];
+}
+
+export function buildCSP(options: CSPOptions = {}): string {
+  const directives: Record<string, string[]> = { ...BASE_DIRECTIVES };
+
+  if (options.serviceUrl) {
+    directives["img-src"] = [...directives["img-src"], options.serviceUrl];
+  }
+
+  if (options.iframeOrigins && options.iframeOrigins.length > 0) {
+    directives["frame-ancestors"] = [...options.iframeOrigins];
+  }
+
+  return serializeCSP(directives);
+}
+
+function serializeCSP(directives: Record<string, string[]>): string {
+  return Object.entries(directives)
+    .map(([key, values]) => [key, ...values].join(" "))
+    .join("; ");
+}

apps/login/src/lib/server/flow-initiation.ts

@@ -19,14 +19,35 @@ import { CreateCallbackRequestSchema, SessionSchema } from "@zitadel/proto/zitad
 import { CreateResponseRequestSchema } from "@zitadel/proto/zitadel/saml/v2/saml_service_pb";
 import { Session } from "@zitadel/proto/zitadel/session/v2/session_pb";
 import { IdentityProviderType } from "@zitadel/proto/zitadel/settings/v2/login_settings_pb";
+import { SecuritySettings } from "@zitadel/proto/zitadel/settings/v2/security_settings_pb";
 import { NextRequest, NextResponse } from "next/server";
-import { DEFAULT_CSP } from "../../../constants/csp";
+import { buildCSP } from "../csp";
 import escapeHtml from "escape-html";
 
 const ORG_SCOPE_REGEX = /urn:zitadel:iam:org:id:([0-9]+)/;
 const ORG_DOMAIN_SCOPE_REGEX = /urn:zitadel:iam:org:domain:primary:(.+)/;
 const IDP_SCOPE_REGEX = /urn:zitadel:iam:org:idp:id:(.+)/;
 
+function setCSPHeaders(
+  response: NextResponse,
+  serviceConfig: ServiceConfig,
+  securitySettings: SecuritySettings | undefined,
+): void {
+  const iframeOrigins =
+    securitySettings?.embeddedIframe?.enabled && securitySettings.embeddedIframe.allowedOrigins.length > 0
+      ? securitySettings.embeddedIframe.allowedOrigins
+      : undefined;
+
+  response.headers.set(
+    "Content-Security-Policy",
+    buildCSP({ serviceUrl: serviceConfig.baseUrl, iframeOrigins }),
+  );
+
+  if (!iframeOrigins) {
+    response.headers.set("X-Frame-Options", "deny");
+  }
+}
+
 const gotoAccounts = ({
   request,
   requestId,
@@ -240,15 +261,7 @@ export async function handleOIDCFlowInitiation(params: FlowInitiationParams): Pr
       const selectedSession = await findValidSession({ serviceConfig, sessions, authRequest });
 
       const noSessionResponse = NextResponse.json({ error: "No active session found" }, { status: 400 });
-
-      if (securitySettings?.embeddedIframe?.enabled) {
-        securitySettings.embeddedIframe.allowedOrigins;
-        noSessionResponse.headers.set(
-          "Content-Security-Policy",
-          `${DEFAULT_CSP} frame-ancestors ${securitySettings.embeddedIframe.allowedOrigins.join(" ")};`,
-        );
-        noSessionResponse.headers.delete("X-Frame-Options");
-      }
+      setCSPHeaders(noSessionResponse, serviceConfig, securitySettings);
 
       if (!selectedSession || !selectedSession.id) {
         return noSessionResponse;
@@ -277,15 +290,7 @@ export async function handleOIDCFlowInitiation(params: FlowInitiationParams): Pr
       });
 
       const callbackResponse = NextResponse.redirect(callbackUrl);
-
-      if (securitySettings?.embeddedIframe?.enabled) {
-        securitySettings.embeddedIframe.allowedOrigins;
-        callbackResponse.headers.set(
-          "Content-Security-Policy",
-          `${DEFAULT_CSP} frame-ancestors ${securitySettings.embeddedIframe.allowedOrigins.join(" ")};`,
-        );
-        callbackResponse.headers.delete("X-Frame-Options");
-      }
+      setCSPHeaders(callbackResponse, serviceConfig, securitySettings);
 
       return callbackResponse;
     } else {

apps/login/src/middleware.ts

@@ -2,7 +2,7 @@ import { SecuritySettings } from "@zitadel/proto/zitadel/settings/v2/security_se
 
 import { headers } from "next/headers";
 import { NextRequest, NextResponse } from "next/server";
-import { DEFAULT_CSP } from "../constants/csp";
+import { buildCSP } from "./lib/csp";
 import { getServiceConfig } from "./lib/service-url";
 export const config = {
   matcher: ["/.well-known/:path*", "/oauth/:path*", "/oidc/:path*", "/idps/callback/:path*", "/saml/:path*", "/:path*"],
@@ -66,12 +66,15 @@ export async function middleware(request: NextRequest) {
 
   const securitySettings = await loadSecuritySettings(request);
 
-  if (securitySettings?.embeddedIframe?.enabled) {
-    responseHeaders.set(
-      "Content-Security-Policy",
-      `${DEFAULT_CSP} frame-ancestors ${securitySettings.embeddedIframe.allowedOrigins.join(" ")};`,
-    );
-    responseHeaders.delete("X-Frame-Options");
+  const iframeOrigins =
+    securitySettings?.embeddedIframe?.enabled && securitySettings.embeddedIframe.allowedOrigins.length > 0
+      ? securitySettings.embeddedIframe.allowedOrigins
+      : undefined;
+
+  responseHeaders.set("Content-Security-Policy", buildCSP({ serviceUrl: serviceConfig.baseUrl, iframeOrigins }));
+
+  if (!iframeOrigins) {
+    responseHeaders.set("X-Frame-Options", "deny");
   }
 
   request.nextUrl.href = `${serviceConfig.baseUrl}${request.nextUrl.pathname}${request.nextUrl.search}`;