Polar

To use Polar sign in, you need to create an OAuth 2.0 Client. You can get your credentials from the [Polar User Settings](https://polar.sh/dashboard/account/developer).

1. Go to your [Polar User Settings](https://polar.sh/settings#oauth)

2. Click "Create OAuth Client"

3. Fill in the required fields:
   * **Application Name**: The name shown to users during authorization
   * **Client Type**: Choose the appropriate client type for your application
   * **Redirect URIs**: Set to `http://localhost:3000/api/auth/callback/polar` for local development. For production, set it to `https://yourdomain.com/api/auth/callback/polar`. If you change the base path of the auth routes, update the redirect URI accordingly.
   * **Scopes**: Select the permissions your application needs (openid, profile, email are default)
   * **Homepage URL**: Your application's main URL

4. Optionally, add:
   * Logo for your application
   * Terms of service URL
   * Privacy policy URL

5. After creation, copy the Client ID and Client Secret to your environment variables. Keep these credentials secure.

To configure the provider, you need to import the provider and pass it to the `socialProviders` option of the auth instance.

```ts title="auth.ts"
import { betterAuth } from "better-auth"

export const auth = betterAuth({
    socialProviders: {
        polar: { // [!code highlight]
            clientId: process.env.POLAR_CLIENT_ID as string, // [!code highlight]
            clientSecret: process.env.POLAR_CLIENT_SECRET as string, // [!code highlight]
        }, // [!code highlight]
    },
})
```

To sign in with Polar, you can use the `signIn.social` function provided by the client, where the `provider` should be set to `polar`.

```ts title="auth-client.ts"
import { createAuthClient } from "better-auth/client"
const authClient = createAuthClient()

const signIn = async () => {
    const data = await authClient.signIn.social({
        provider: "polar"
    })
}
```