OAuth invalid redirect_uri

[tydolla00]

---

Summary

Clicking Sign in with GitHub shows GitHub’s warning page: Be careful! The redirect_uri is not associated with this application. Inspecting the authorize request shows Better Auth is sending redirect_uri=%2Fcallback%2Fgithub, i.e. a relative path.

I’m attempting to follow the next-auth migration guide and believe I’ve successfully set it up. However, for some reason, my redirect URI is invalid. I’m at a loss as to what’s causing this issue. I’ve tried using incognito mode, different browsers, and clearing my cache, but none of these methods seem to resolve the problem. I’ve configured my next app with the URL NEXT_PUBLIC_APP_URL=http://localhost:3000. Both Google and GitHub are configured to http://localhost:3000/api/auth/callback/google and http://localhost:3000/api/auth/callback/github, respectively, through their OAuth configurations.

https://github.com/login/oauth/authorize?response_type=code&client_id=${clientId}&scope=read%3Auser+user%3Aemail&redirect_uri=%2Fcallback%2Fgithub

Because the redirect URI no longer matches the fully qualified URL we have registered in the GitHub OAuth app, GitHub blocks the flow.

Actual Behavior

• GitHub rejects the OAuth request, warning that the supplied redirect_uri is not associated with the application because Better Auth encoded /callback/github instead of an absolute URL.
• Attempting to sign in with Google now yields Access blocked: Authorization Error – Error 400: invalid_request with redirect_uri=/callback/google and flowName=GeneralOAuthFlow, so both providers appear to be affected by the relative redirect.

Expected Behavior

Better Auth should send the fully qualified callback URL (e.g. https://localhost:3000/api/auth/callback/{provider}, matching the value registered with the provider), so the OAuth exchange can finish successfully.

Relevant Configuration

// src/lib/auth.ts
import { betterAuth } from "better-auth";
...
export const auth = betterAuth({
  ...
  socialProviders: {
    github: {
      clientId: config.AUTH_GITHUB_ID!,
      clientSecret: config.AUTH_GITHUB_SECRET!,
      // redirectUri: "http://localhost:3000/api/auth/callback/github",
    },
    google: {
      clientId: config.AUTH_GOOGLE_ID!,
      clientSecret: config.AUTH_GOOGLE_SECRET!,
    },
  },
  plugins: [nextCookies()],
});

Because the explicit redirectUri is commented out, Better Auth appears to fall back to /callback/{provider} rather than inferring the deployed base URL. GitHub rejects the relative path immediately, and Google now responds with invalid_request.

Additional Context

• Browser: Chrome 131.0.6778.265
• OS: macOS 15.1 (Apple Silicon)

[better-auth-agent]

Hi there, thanks for raising the issue! It looks like Better Auth is defaulting to a relative callback path because the explicit redirectUri is commented out. To resolve the problem, please try the following steps:

1. Uncomment or explicitly set the redirectUri for each provider using the fully qualified URL (e.g. "http://localhost:3000/api/auth/callback/github"). This ensures the OAuth flow uses an absolute URL that matches your registered settings [1].

2. Double-check that your NEXT_PUBLIC_APP_URL is correctly set and that no other configuration overrides the redirect URIs.

3. Verify that any plugins (like nextCookies) aren’t interfering with the expected base URL resolution.

Does this help clarify the next steps? Tag @better-auth-agent if you would like an answer from the Agent.

Diagram • Discord • GitHub

[tydolla00]

@better-auth-agent uncommenting out the redirect uri line does not work and gives the same error.

[better-auth-agent]

It sounds like Better Auth is still defaulting to a relative path even when you try to override it. Our documentation shows that you can set a fully qualified URL in the socialProviders configuration (for example, "http://localhost:3000/api/auth/callback/github") to ensure that the callback matches what you’ve registered with GitHub [1]. Since uncommenting the redirectUri field did not resolve the issue, please verify that your NEXT_PUBLIC_APP_URL environment variable is being properly injected into your build and that it matches exactly the URL you have configured in your GitHub app. Also, double-check if any middleware or plugin (such as your nextCookies plugin) might be inadvertently overriding the computed redirect URL.

Have you confirmed that your environment variables are available at runtime and match your configuration in both Better Auth and GitHub? Tag @better-auth-agent if you would like an answer from the Agent.

Diagram • Discord • GitHub

[akhansari]

I have a similar issue, but the generated URI is http and not https.

[aoifelee]

I am also seeing this issue. Basically the exact same thing as the original reporter.

[ping-maxwell]

Hello @akhansari @aoifelee things are working fine on my end on latest. Do you guys by chance have a public repository which I can check out? or maybe if possible, if someone can provide a minimal reproduction repo for me to test?

[akhansari]

@ping-maxwell I no longer have it with the latest version, thank you ✨