fix(login): allow custom protocols for native apps again (#12332)

# Which Problems Are Solved

- Native apps (mobile/desktop) use custom protocol schemes (e.g.
`myapp://callback`, `io.zitadel.app://auth`) as OAuth/OIDC redirect
URIs. The previous redirect-safety check in the login UI only allowed
`http:`/`https:` absolute URLs, so these custom-scheme callbacks were
wrongly rejected and native app login flows were broken.
- Even for valid external redirects, `router.push()` triggers an RSC
prefetch `fetch()` that is blocked by the CSP `connect-src 'self'`
directive for non-same-origin URLs, so navigation to
external/custom-protocol targets failed.
- SAML and OIDC callback URLs returned from the backend were not
consistently validated before being used for redirects/POSTs across the
various flow entry points.

# How the Problems Are Solved

- Reworked `isSafeRedirectUri` to use `@braintree/sanitize-url` instead
of a strict `http/https`-only allowlist. Custom protocol schemes are now
permitted, while dangerous schemes (`javascript:`, `data:`, plus an
explicit block of `file:`, `blob:`, `about:`) are still rejected.
- Added `isExternalUrl` helper to distinguish internal relative paths
(`/...`) from external/custom-protocol targets.
- In `handleServerActionResponse`, external/custom-protocol redirects
now navigate via `window.location.href` (full navigation) instead of
`router.push()`, avoiding the CSP-blocked RSC prefetch. Internal paths
continue to use `router.push()`.
- Added consistent redirect-URI validation for SAML and OIDC callbacks
across all relevant entry points (`oidc.ts`, `saml.ts`,
`server/flow-initiation.ts` including the `prompt=none` path, and the
SAML `samlData` POST case), blocking unsafe URLs with a clear warning
and error response.

# Additional Changes

- Added `@braintree/sanitize-url` (`^7.1.2`) dependency to `apps/login`
(`package.json` / `pnpm-lock.yaml`).
- Added unit tests for `isExternalUrl` covering relative paths, absolute
HTTP/HTTPS URLs, custom protocol schemes, and protocol-relative URLs.
- Annotated the intentional `window.location.href` navigation with a
CodeQL suppression comment, documenting that the URL is validated by
`isSafeRedirectUri` beforehand.
- Minor formatting cleanup in `console` JWT provider component.

# Additional Context

- This restores behavior that previously worked for native apps but
regressed when redirect validation was tightened to `http`/`https` only.

---------

Co-authored-by: Max Peintner <[email protected]>

apps/login/package.json

@@ -23,6 +23,7 @@
     "*": "prettier --write --ignore-unknown"
   },
   "dependencies": {
+    "@braintree/sanitize-url": "^7.1.2",
     "@connectrpc/connect": "^2.1.1",
     "@connectrpc/connect-node": "^2.1.1",
     "@headlessui/react": "^2.2.10",

apps/login/src/lib/client-utils.test.ts

@@ -1,5 +1,5 @@
 import { beforeEach, describe, expect, test, vi } from "vitest";
-import { isSafeRedirectUri } from "./client-utils";
+import { isExternalUrl, isSafeRedirectUri } from "./client-utils";
 
 describe("isSafeRedirectUri", () => {
   beforeEach(() => {
@@ -42,3 +42,35 @@ describe("isSafeRedirectUri", () => {
     expect(await isSafeRedirectUri("http://%")).toBe(false);
   });
 });
+
+describe("isExternalUrl", () => {
+  test("should return false for relative paths", () => {
+    expect(isExternalUrl("/dashboard")).toBe(false);
+    expect(isExternalUrl("/ui/console")).toBe(false);
+    expect(isExternalUrl("/")).toBe(false);
+    expect(isExternalUrl("/[email protected]")).toBe(false);
+    expect(isExternalUrl("/signedin?sessionId=123&organization=456")).toBe(false);
+  });
+
+  test("should return true for absolute HTTPS URLs", () => {
+    expect(isExternalUrl("https://example.com/callback")).toBe(true);
+    expect(isExternalUrl("https://my-zitadel.com/ui/console")).toBe(true);
+  });
+
+  test("should return true for absolute HTTP URLs", () => {
+    expect(isExternalUrl("http://localhost:3000/callback")).toBe(true);
+    expect(isExternalUrl("http://example.com")).toBe(true);
+  });
+
+  test("should return true for custom protocol schemes (native apps)", () => {
+    expect(isExternalUrl("myapp://callback")).toBe(true);
+    expect(isExternalUrl("com.example.app://oauth/callback")).toBe(true);
+    expect(isExternalUrl("io.zitadel.app://auth")).toBe(true);
+    expect(isExternalUrl("flutter-app://callback?code=abc&state=xyz")).toBe(true);
+  });
+
+  test("should return true for protocol-relative URLs", () => {
+    expect(isExternalUrl("//evil.com")).toBe(true);
+    expect(isExternalUrl("//example.com/path")).toBe(true);
+  });
+});

apps/login/src/lib/client-utils.ts

@@ -1,3 +1,5 @@
+import { sanitizeUrl } from "@braintree/sanitize-url";
+
 export type ServerActionResponse =
   | { redirect: string }
   | { error: string }
@@ -17,7 +19,16 @@ export function handleServerActionResponse(
 
   if ("redirect" in response && response.redirect) {
     if (isSafeRedirectUri(response.redirect)) {
-      router.push(response.redirect);
+      if (typeof window !== "undefined" && isExternalUrl(response.redirect)) {
+        // External/custom-protocol URLs: use window.location for full navigation.
+        // router.push() would trigger an RSC prefetch fetch() that gets blocked
+        // by CSP connect-src 'self' for non-same-origin URLs.
+        // CodeQL: This is safe — the URL is validated by isSafeRedirectUri above,
+        // which blocks javascript:, data:, file:, blob:, and about: schemes.
+        window.location.href = response.redirect; // lgtm[js/client-side-unvalidated-url-redirection]
+      } else {
+        router.push(response.redirect);
+      }
       return true;
     } else {
       console.warn("handleServerActionResponse: Blocked unsafe redirect URI:", response.redirect);
@@ -27,8 +38,14 @@ export function handleServerActionResponse(
   }
 
   if ("samlData" in response && response.samlData) {
-    setSamlData(response.samlData);
-    return true;
+    if (isSafeRedirectUri(response.samlData.url)) {
+      setSamlData(response.samlData);
+      return true;
+    } else {
+      console.warn("handleServerActionResponse: Blocked unsafe SAML post URL:", response.samlData.url);
+      setError("Unsafe redirect URI was blocked");
+      return true;
+    }
   }
 
   if ("error" in response && response.error) {
@@ -39,6 +56,20 @@ export function handleServerActionResponse(
   return false;
 }
 
+/**
+ * Returns true if the URL is external (absolute URL or custom protocol).
+ * Relative paths (starting with "/" but not "//") are considered internal.
+ */
+export function isExternalUrl(url: string): boolean {
+  if (url.startsWith("/") && !url.startsWith("//")) {
+    return false;
+  }
+  return true;
+}
+
+const SANITIZE_BLANK = "about:blank";
+const EXTRA_BLOCKED = new Set(["file:", "blob:", "about:"]);
+
 /**
  * Validates whether a given redirect URI is safe.
  * Safe URIs are either relative paths or absolute URLs matching the current host.
@@ -52,19 +83,13 @@ export function isSafeRedirectUri(uri: string): boolean {
     return true;
   }
 
-  // 2. Check absolute URLs for safe protocols (http/https)
-  // We allow external domains, but strictly forbid javascript:/data: etc.
+  const sanitized = sanitizeUrl(uri);
+  if (sanitized === SANITIZE_BLANK) return false;
+
   try {
-    const parsedUri = new URL(uri);
-
-    // Only allow http(s) protocols
-    if (parsedUri.protocol !== "http:" && parsedUri.protocol !== "https:") {
-      return false;
-    }
-
-    return true;
+    const parsed = new URL(sanitized);
+    return !EXTRA_BLOCKED.has(parsed.protocol);
   } catch {
-    // If it can't be parsed as a URL and didn't start with /, it's unsafe
     return false;
   }
 }

apps/login/src/lib/oidc.ts

@@ -65,6 +65,10 @@ export async function loginWithOIDCAndSession({
           }),
         });
         if (callbackUrl) {
+          if (!isSafeRedirectUri(callbackUrl)) {
+            console.warn("loginWithOIDCAndSession: Blocked unsafe OIDC callback URL:", callbackUrl);
+            return { error: "Unsafe redirect URI was blocked" };
+          }
           return { redirect: callbackUrl };
         } else {
           return { error: "An error occurred!" };

apps/login/src/lib/saml.ts

@@ -73,8 +73,16 @@ export async function loginWithSAMLAndSession({
           }),
         });
         if (url && binding.case === "redirect") {
+          if (!isSafeRedirectUri(url)) {
+            console.warn("loginWithSAMLAndSession: Blocked unsafe SAML redirect URL:", url);
+            return { error: "Unsafe redirect URI was blocked" };
+          }
           return { redirect: url };
         } else if (url && binding.case === "post") {
+          if (!isSafeRedirectUri(url)) {
+            console.warn("loginWithSAMLAndSession: Blocked unsafe SAML post URL:", url);
+            return { error: "Unsafe redirect URI was blocked" };
+          }
           return {
             samlData: {
               url,

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

@@ -1,4 +1,5 @@
 import { getValidLocaleFromUILocales } from "@/lib/auth-utils";
+import { isSafeRedirectUri } from "@/lib/client-utils";
 import { getLanguageCookie, setLanguageCookie } from "@/lib/cookies";
 
 import { shouldUILocalesOverrideCookie } from "@/lib/i18n";
@@ -306,6 +307,10 @@ export async function handleOIDCFlowInitiation(params: FlowInitiationParams): Pr
         }),
       });
 
+      if (!isSafeRedirectUri(callbackUrl)) {
+        logger.warn("Blocked unsafe OIDC callback URL (prompt=none)", { callbackUrl });
+        return NextResponse.json({ error: "Unsafe redirect URI was blocked" }, { status: 400 });
+      }
       const callbackResponse = NextResponse.redirect(callbackUrl);
       setCSPHeaders(callbackResponse, serviceConfig, securitySettings);
       return callbackResponse;
@@ -347,6 +352,10 @@ export async function handleOIDCFlowInitiation(params: FlowInitiationParams): Pr
           }),
         });
         if (callbackUrl) {
+          if (!isSafeRedirectUri(callbackUrl)) {
+            logger.warn("Blocked unsafe OIDC callback URL", { callbackUrl });
+            return NextResponse.json({ error: "Unsafe redirect URI was blocked" }, { status: 400 });
+          }
           return NextResponse.redirect(callbackUrl);
         } else {
           logger.info("could not create callback, redirect user to choose other account");
@@ -446,8 +455,16 @@ export async function handleSAMLFlowInitiation(params: FlowInitiationParams): Pr
     });
 
     if (url && binding.case === "redirect") {
+      if (!isSafeRedirectUri(url)) {
+        logger.warn("Blocked unsafe SAML redirect URL", { url });
+        return NextResponse.json({ error: "Unsafe redirect URI was blocked" }, { status: 400 });
+      }
       return NextResponse.redirect(url);
     } else if (url && binding.case === "post") {
+      if (!isSafeRedirectUri(url)) {
+        logger.warn("Blocked unsafe SAML post URL", { url });
+        return NextResponse.json({ error: "Unsafe redirect URI was blocked" }, { status: 400 });
+      }
       const html = `
         <html>
           <body onload="document.forms[0].submit()">

console/src/app/modules/providers/provider-jwt/provider-jwt.component.ts

@@ -117,7 +117,7 @@ export class ProviderJWTComponent {
       issuer: new UntypedFormControl('', [requiredValidator]),
       jwtEndpoint: new UntypedFormControl('', [requiredValidator]),
       keysEndpoint: new UntypedFormControl('', [requiredValidator]),
-      audience: new UntypedFormControl('' ),
+      audience: new UntypedFormControl(''),
     });
 
     this.authService

pnpm-lock.yaml

@@ -208,6 +208,9 @@ importers:
 
   apps/login:
     dependencies:
+      '@braintree/sanitize-url':
+        specifier: ^7.1.2
+        version: 7.1.2
       '@connectrpc/connect':
         specifier: ^2.1.1
         version: 2.1.1(@bufbuild/[email protected])
@@ -975,6 +978,7 @@ packages:
   '@angular/[email protected]':
     resolution: {integrity: sha512-9WLnsJE0xqtd1rVtHMvsAUxFy3OdPks4bdmUIqyw23X/je7ytUALAGWNadffcZBwRpa1A6TUnLr9X4+Draz3kw==}
     engines: {node: ^20.19.0 || ^22.12.0 || >=24.0.0}
+    deprecated: '@angular/animations is deprecated. Use `animate.enter` and `animate.leave` instead. For more information see: https://v22.angular.dev/guide/animations.'
     peerDependencies:
       '@angular/core': 21.2.14
 
@@ -1105,6 +1109,7 @@ packages:
   '@angular/[email protected]':
     resolution: {integrity: sha512-m5U4zX8JFnxTAIGpsBXIAyefSmYqdORY/OfHC0aMmZovuFCbXXIYqYRQDBB7+YVNpSDSHllCrKEZFu/CC6dq3g==}
     engines: {node: ^20.19.0 || ^22.12.0 || >=24.0.0}
+    deprecated: '@angular/platform-browser-dynamic is deprecated. Use `@angular/platform-browser` instead.'
     peerDependencies:
       '@angular/common': 21.2.14
       '@angular/compiler': 21.2.14
@@ -1308,6 +1313,9 @@ packages:
   '@balena/[email protected]':
     resolution: {integrity: sha512-wMue2Sy4GAVTk6Ic4tJVcnfdau+gx2EnG7S+uAEe+TWJFqE4YoWN4/H8MSLj4eYJKxGg26lZwboEniNiNwZQ6Q==}
 
+  '@braintree/[email protected]':
+    resolution: {integrity: sha512-jigsZK+sMF/cuiB7sERuo9V7N9jx+dhmHHnQyDSVdpZwVutaBu7WvNYqMDLSgFgfB30n452TP3vjDAvFC973mA==}
+
   '@bufbuild/[email protected]':
     resolution: {integrity: sha512-c7owUswBbMmwfHPH9JRBEJu09mrXYGC33V2JQCgraWCBm74Z95AOkhDua50qiBrQnysvJkJ0p/z4MWxJqcpnIA==}
     engines: {node: '>=12'}
@@ -13140,6 +13148,8 @@ snapshots:
 
   '@balena/[email protected]': {}
 
+  '@braintree/[email protected]': {}
+
   '@bufbuild/[email protected]':
     optional: true