Kinde•5mo ago

UnhandledPromiseRejection on login redirect with SvelteKit

Hello KindeAuth Team,

I request your help getting the login redirect to work.

I am trying to Redirect to a different page upon login, but receive an UnhandledPromiseRejection error.
My other normal redirects within the application work normally.

When I remove the redirect URL from Kinde's "Allowed callback URLs" the error goes way, but I get redirected to the home page.

Tech: NodeJs 24.4.1, SvelteKit 5, latest KindeAuth

"svelte": "^5.37.1",
"@sveltejs/kit": "^2.26.1",
"@kinde-oss/kinde-auth-sveltekit": "^2.2.2",
"@kinde/webhooks": "^1.0.0",
"@kitql/handles": "^0.3.0",
"@inlang/cli": "^3.0.12",
"@inlang/paraglide-js": "2.2.0",
etc.

I receive the following error:

node:internal/process/promises:392
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

node:internal/process/promises:392
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

node:internal/process/promises:392
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

node:internal/process/promises:392
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

Here is my login link with the problematic redirect:

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">
Login
</a>

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">
Login
</a>

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">
Login
</a>

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">
Login
</a>

`

I will post the request of the code in the next posting.

I tried quite a few fixes and searched online, but I have yet to find a solution that works.

Much appreciate your support and help!

Paul

Paul EOP•7/29/25, 1:32 PM

My Kinde Auth setup:

// src/routes/api/auth/[...kindeAuth]/+server.ts
import {handleAuth} from '@kinde-oss/kinde-auth-sveltekit';
import type {RequestEvent} from '@sveltejs/kit';

export function GET(requestEvents: RequestEvent) {
    return handleAuth(requestEvents);
}

// src/routes/api/auth/[...kindeAuth]/+server.ts
import {handleAuth} from '@kinde-oss/kinde-auth-sveltekit';
import type {RequestEvent} from '@sveltejs/kit';

export function GET(requestEvents: RequestEvent) {
    return handleAuth(requestEvents);
}

// src/hooks.server.ts
// import { isRedirect } from '@sveltejs/kit';

// process.on('unhandledRejection', (reason) => {
//     // swallow only Redirect objects that leak out of Kinde
//     if (isRedirect(reason)) return;            // OK, ignore
//     throw reason;                              // everything else: crash as usual
// });

import type { Handle } from '@sveltejs/kit';
import { sequence } from '@sveltejs/kit/hooks';
import { paraglideMiddleware } from '$lib/paraglide/server';
import { sessionHooks } from '@kinde-oss/kinde-auth-sveltekit';
import { handleCsrf } from '@kitql/handles';

// Kinde middleware handle adapted to SvelteKit's Handle type
const kindeHandle: Handle = async ({ event, resolve }) => {
    sessionHooks({ event: event as any });
    return await resolve(event);
};

// Paraglide middleware handle
const paraglideHandle: Handle = ({ event, resolve }) =>
    paraglideMiddleware(event.request, ({ locale }) =>
        resolve(event, {
            transformPageChunk: ({ html }) => html.replace('%lang%', locale)
        })
    );

// Configure CSRF protection with webhook bypass using KitQL
const csrfHandle = handleCsrf([
    // Allow Kinde webhooks from any origin (they use JWT verification for security)
    ['/api/webhooks/kinde', { origin: true }]
]);

// Combine all handlers using sequence
export const handle: Handle = sequence(csrfHandle, kindeHandle, paraglideHandle);

// src/hooks.server.ts
// import { isRedirect } from '@sveltejs/kit';

// process.on('unhandledRejection', (reason) => {
//     // swallow only Redirect objects that leak out of Kinde
//     if (isRedirect(reason)) return;            // OK, ignore
//     throw reason;                              // everything else: crash as usual
// });

import type { Handle } from '@sveltejs/kit';
import { sequence } from '@sveltejs/kit/hooks';
import { paraglideMiddleware } from '$lib/paraglide/server';
import { sessionHooks } from '@kinde-oss/kinde-auth-sveltekit';
import { handleCsrf } from '@kitql/handles';

// Kinde middleware handle adapted to SvelteKit's Handle type
const kindeHandle: Handle = async ({ event, resolve }) => {
    sessionHooks({ event: event as any });
    return await resolve(event);
};

// Paraglide middleware handle
const paraglideHandle: Handle = ({ event, resolve }) =>
    paraglideMiddleware(event.request, ({ locale }) =>
        resolve(event, {
            transformPageChunk: ({ html }) => html.replace('%lang%', locale)
        })
    );

// Configure CSRF protection with webhook bypass using KitQL
const csrfHandle = handleCsrf([
    // Allow Kinde webhooks from any origin (they use JWT verification for security)
    ['/api/webhooks/kinde', { origin: true }]
]);

// Combine all handlers using sequence
export const handle: Handle = sequence(csrfHandle, kindeHandle, paraglideHandle);

Paul EOP•7/29/25, 1:57 PM

ChatGPT said that this is known and that there should be a fix in @kinde-oss/kinde-auth-sveltekit ≥ 2.3.x ; but maybe he halucinated this?

Paul EOP•7/29/25, 2:03 PM

ChatGPT also said that here: https://github.com/kinde-oss/kinde-sveltekit-sdk/blob/main/src/lib/handleAuth/handleAuth.ts

redirectToPostLoginUrl(); should be awaited:
await redirectToPostLoginUrl();

similiar to: await openPortal(request, options);

Not sure if he is right; but looks like a logical fix.

GitHub

kinde-sveltekit-sdk/src/lib/handleAuth/handleAuth.ts at main · kin...

Contribute to kinde-oss/kinde-sveltekit-sdk development by creating an account on GitHub.

AbdiwakAPP•7/29/25, 2:22 PM

Hi Paul, Thanks for reaching out.

The issue comes from how redirections are handled after login and how SvelteKit treats redirects inside server routes.

Here's what need to be done:

Only include the callback URL in Kinde

http://localhost:5173/api/auth/kinde_callback

http://localhost:5173/api/auth/kinde_callback

Don’t add any page like /myother/testpage/myother/testpage there, that page is not supposed to handle the OAuth response directly.

Post_login_redirect_url is the correct way
Your current link is right:

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">Login</a>

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">Login</a>

After logging in, Kinde will send users to /api/auth/kinde_callback/api/auth/kinde_callback, and from there, the SDK will automatically forward them to /myother/testpage/myother/testpage.

**That error message (**`UnhandledPromiseRejection: "#<Redirect>"`**)** This error comes from how SvelteKit logs redirects inside server routes (like `/api/auth`). It's not a breaking issue and the redirect should still happen normally in the browser.If you want to suppress the warning during development, you can add this in `hooks.server.ts` (you already commented it out):

import { isRedirect } from '@sveltejs/kit';

process.on('unhandledRejection', (reason) => {
  if (isRedirect(reason)) return; // ignore expected redirects
  throw reason; // log everything else
});

import { isRedirect } from '@sveltejs/kit';

process.on('unhandledRejection', (reason) => {
  if (isRedirect(reason)) return; // ignore expected redirects
  throw reason; // log everything else
});

Let me know if I need to clarify anything,
Thanks

AAbdiwak Hi Paul, Thanks for reaching out. The issue comes from how redirections ar...

Paul EOP•7/29/25, 3:33 PM

Hi Abdiwak, thank you too!

Oh, I had the following:
http://localhost:5173
http://localhost:5173/api/auth/kinde_callback
http://localhost:5173/myother/testpage

I will change this to only include:
http://localhost:5173/api/auth/kinde_callback

The UI on kinde.com says the following:
"These are the redirect URIs where the user can be sent after authenticating. Add each URL on a new line."

Reading this, I thought these would be the post login redirect urls.

Good!
I see, then I will ignore expected redirects/unhandledRejections.

Maybe you could include this in your Svelte Starter Kit?

My issue issue is now, that it is not redirecting to /myother/testpage but to /

Thank you

AbdiwakAPP•7/29/25, 4:52 PM

Thanks Again

If your app is redirecting to

instead of /myother/testpage/myother/testpage, there are a few things to check:

Check your login link:
Your login link should look like this:

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">Login</a>

<a href="/api/auth/login?post_login_redirect_url=/myother/testpage">Login</a>

This tells the SDK to redirect to /myother/testpage/myother/testpage after login.

**Check your environment variables:**
- KINDE_REDIRECT_URLKINDE_REDIRECT_URL should be http://localhost:5173/api/auth/kinde_callbackhttp://localhost:5173/api/auth/kinde_callback
- KINDE_POST_LOGIN_REDIRECT_URLKINDE_POST_LOGIN_REDIRECT_URL should be set to your default landing page, e.g., http://localhost:5173/http://localhost:5173/ (this is used only if post_login_redirect_urlpost_login_redirect_url is not set in the login link)

Ensure you are using the latest SDK and following the documented integration pattern. And also ensure that there are no typos or case mismatches in the URL and no custom logic in your callback handler that could override the redirect.

Let me know if this helps, Thanks

Paul EOP•7/29/25, 7:26 PM

The login URL looks fine, this is the actual link:```html<a href="/api/auth/login?post_login_redirect_url=/become-teacher/apply" >Login</a>````
These look fine:KINDE_REDIRECT_URL=http://localhost:5173/api/auth/kinde_callbackKINDE_POST_LOGOUT_REDIRECT_URL=http://localhost:5173KINDE_POST_LOGIN_REDIRECT_URL=http://localhost:5173

I am using the latest SDK.
My callback handler is customized.

What I will try next is to checkout your Svelte Starter sample and see whether I get it working there!

Thank you

Paul EOP•7/30/25, 7:37 AM

Hello Abidiwak,

I checked out your Kinde Svelte Starter Kit.

Without modifications, but just adding a login URL with redirect to another new page /dashboard/mypage, the post login redirect works as expected.

But, after upgrading all dependencies to latest versions, I get the UnhandledPromiseRejection error and node crashes.

I mananaged to isolate it to @kinde-oss/kinde-auth-sveltekit

2.1.0 works:

"dependencies": {
"@kinde-oss/kinde-auth-sveltekit": "2.1.0"
},

2.2.2 causes the issue:

"dependencies": {
"@kinde-oss/kinde-auth-sveltekit": "2.2.2"
},

I verified this multiple times.

I attached an image with a possible cause of this issue. See: https://github.com/kinde-oss/kinde-sveltekit-sdk/compare/2.1.0...2.2.1#diff-3edd8e776bc1bee6fb1faacea7a02ff11827bd8e2e54a180579c1bcb6a99cbb9

Here is the error message again:

node:internal/process/promises:392
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

node:internal/process/promises:392
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

GitHub

Comparing 2.1.0...2.2.1 · kinde-oss/kinde-sveltekit-sdk

Contribute to kinde-oss/kinde-sveltekit-sdk development by creating an account on GitHub.

Paul EOP•7/30/25, 7:38 AM

Adding the unhandledRejection, this error goes away, but now I am redirected to / instead of /dashboard/mypage

import { isRedirect } from '@sveltejs/kit';

process.on('unhandledRejection', (reason) => {
  if (isRedirect(reason)) {
        console.warn('Swallowing benign redirect error:', reason);
        return; // ignore expected redirects
    }

  throw reason; // log everything else
});

import { isRedirect } from '@sveltejs/kit';

process.on('unhandledRejection', (reason) => {
  if (isRedirect(reason)) {
        console.warn('Swallowing benign redirect error:', reason);
        return; // ignore expected redirects
    }

  throw reason; // log everything else
});

``

On a side note I also see following error, not sure if it is related:

ERROR Flag feature Error: Flag theme was not found, and no default value has been provided
    at file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:58:27
    at step (file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:32:23)
    at Object.next (file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:13:53)
    at fulfilled (file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:4:58)

ERROR Flag feature Error: Flag theme was not found, and no default value has been provided
    at file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:58:27
    at step (file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:32:23)
    at Object.next (file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:13:53)
    at fulfilled (file:///Users/paule/Dev/kinde-test/kinde-sveltekit-starter-kit/node_modules/@kinde-oss/kinde-typescript-sdk/dist/sdk/utilities/feature-flags.js:4:58)

Paul EOP•7/30/25, 7:42 AM

I tried including the full packages.json here, but Discord doesnt want me to send such a large message.

Much appreciated

Paul

AbdiwakAPP•8/1/25, 1:56 AM

Hi, Paul
I will get back to you on this shortly. I'm cross-checking this with the internal team. Thanks for your patience!

Paul EOP•8/5/25, 8:57 PM

Hi Abdiwak, I must report that today in my own app even with "@kinde-oss/kinde-auth-sveltekit" version "2.1.0" the post login redirect doesn't work. Since then I updated to latest dependencies and also nodejs 24.5.0. In your starter kit sample downgrading to 2.1.0 still helps.

Anyway: Updating to latest 2.2.2 and then adjusting following file locally "fixes" the redirect for me:

/node_modules/@kinde-oss/kinde-auth-sveltekit/dist/handleAuth/handleAuth.js

 case "kinde_callback":
            await kindeAuthClient.handleRedirectToApp(request, new URL(request.url));
            redirectToPostLoginUrl();
            return redirect(302, kindeConfiguration.loginRedirectURL ?? "/");

 case "kinde_callback":
            await kindeAuthClient.handleRedirectToApp(request, new URL(request.url));
            redirectToPostLoginUrl();
            return redirect(302, kindeConfiguration.loginRedirectURL ?? "/");

``

to

 case "kinde_callback":
            await kindeAuthClient.handleRedirectToApp(request, new URL(request.url));
            await redirectToPostLoginUrl();
            return redirect(302, kindeConfiguration.loginRedirectURL ?? "/");

 case "kinde_callback":
            await kindeAuthClient.handleRedirectToApp(request, new URL(request.url));
            await redirectToPostLoginUrl();
            return redirect(302, kindeConfiguration.loginRedirectURL ?? "/");

`

Without the await in line 54 I get the UnhandledPromiseRejection error and the redirect doesn't happen:

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "#<Redirect>".
    at throwUnhandledRejectionsMode (node:internal/process/promises:392:7)
    at processPromiseRejections (node:internal/process/promises:475:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:106:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

Since this is just a quickfix for localhost development I hope you can patch this soon

Hope this helps!

Much appreciated,
Paul

AbdiwakAPP•8/7/25, 3:54 PM

Hi Paul,

Thank you so much for digging into this and sharing your findings, this is super helpful!

Our team is investigating this in detail, and I’ll get back to you as soon as we have an update.

Thanks again for your patience and for bringing this to our attention.

Paul EOP•8/19/25, 5:57 PM

Hi @Abdiwak - Kinde! I have been wondering

whether you have any news about the redirects? Thank you too!

AbdiwakAPP•8/22/25, 6:58 AM

Hi there, thanks again for your patience.

We’ve just published @kinde-oss/kinde-auth-sveltekit@2.2.3@kinde-oss/kinde-auth-sveltekit@2.2.3, which includes a fix for the redirect flow you were experiencing. Could you update to this version and try again?

UnhandledPromiseRejection on login redirect with SvelteKit

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