# Authorize

GET

/

oauth

/

authorize

:::code-group
```shellscript title="Browser navigation"
GET https://api.resend.com/oauth/authorize?client_id=550e8400-e29b-41d4-a716-446655440000&response_type=code&redirect_uri=http%3A%2F%2F127.0.0.1%3A49152%2Foauth%2Fcallback&scope=emails%3Asend&state=STATE_VALUE&code_challenge=CODE_CHALLENGE_VALUE&code_challenge_method=S256
```
:::

:::code-group
```http title="Response"
HTTP/1.1 302 Found
Location: https://resend.com/oauth/authorize/3f9c1e2a-...
```
:::

This is a browser redirect endpoint, not a JSON API call. Open this URL in the user’s browser. Don’t fetch it from a backend or CLI process and follow the redirect yourself, since the user has to see and approve the consent screen. The flow:

1. The client opens `/oauth/authorize` in the user’s browser.
2. Resend redirects (`302`) to the Resend dashboard consent screen, which handles login if needed.
3. The user reviews and approves (or denies) the request.
4. The dashboard redirects the browser back to the client’s `redirect_uri` with a `code` and the original `state`.

## Query Parameters

string

required

The `client_id` from [registration](/guides/oauth-register), or the HTTPS URL of a [Client ID Metadata Document](#client-id-metadata-documents). Resend tells the two apart by the `https://` prefix.

string

required

Must be `"code"`.

string

required

Must exactly match one of the client’s registered redirect URIs. The only exception is loopback URIs (`127.0.0.1`, `localhost`, `[::1]`), where the port is allowed to differ from what was registered.

string

Space-delimited list of requested scopes. If omitted, defaults to the client’s full registered scope set.

### Scopes

- `emails:send` is enough for send-only routes: `POST /emails`, `POST /email`, `POST /emails/sending`, `POST /email/sending`, and `POST /broadcasts/:broadcastId/send`.
- `full_access` is required for every other API route. Also satisfies any `emails:send`-scoped check.

string

An opaque value round-tripped back on the callback unchanged. Use it to bind the callback to the request that started the flow. Recommended, not required by the server, but a client that skips it can’t detect CSRF on the callback. Maximum 1024 characters.

string

required

Base64url-encoded SHA-256 hash of a [code\_verifier](/guides/oauth-token#param-code-verifier) your client generates.

string

required

Must be `"S256"`. Resend does not support the `plain` method.

:::callout{intent="info"}
A `resource` parameter (RFC 8707) is accepted but ignored. Resend does not support resource indicators yet.
:::

### Client ID Metadata Documents

A `client_id` that starts with `https://` is read as the URL of a JSON document describing the client, so the client never registers. This follows the [OAuth Client ID Metadata Document](https://datatracker.ietf.org/doc/draft-ietf-oauth-client-id-metadata-document/) draft. This is the only endpoint that fetches the document. See [Client ID Metadata Documents](/guides/tutorials-guides-building-a-resend-oauth-client#client-id-metadata-documents) for the document fields and for how Resend fetches and caches it.

```shellscript
GET https://api.resend.com/oauth/authorize?client_id=550e8400-e29b-41d4-a716-446655440000&response_type=code&redirect_uri=http%3A%2F%2F127.0.0.1%3A49152%2Foauth%2Fcallback&scope=emails%3Asend&state=STATE_VALUE&code_challenge=CODE_CHALLENGE_VALUE&code_challenge_method=S256
```

```http
HTTP/1.1 302 Found
Location: https://resend.com/oauth/authorize/3f9c1e2a-...
```

## Errors

Before `client_id` and `redirect_uri` are validated (unknown `client_id`, invalid or unregistered `redirect_uri`), Resend returns a JSON error body, since it can’t safely redirect to an unvalidated URL. Once Resend validates `client_id` and `redirect_uri`, errors redirect (`302`) back to `redirect_uri` with `error`, `error_description`, and (if provided) `state` as query parameters only when the `redirect_uri` is trusted: a loopback address, a private-use URI scheme, or a verified client. An unverified `https` callback gets a JSON error body instead, which prevents the endpoint from being used as an open redirect. Handle both.

| `error`               | When                                                                                                       |
| --------------------- | ---------------------------------------------------------------------------------------------------------- |
| `invalid_request`     | `response_type` isn’t `code`, or `code_challenge_method` isn’t `S256`.                                     |
| `invalid_client`      | Unknown or disabled `client_id`. Also a metadata document that couldn’t be fetched or didn’t validate.     |
| `unauthorized_client` | The client isn’t registered for the `authorization_code` grant.                                            |
| `invalid_scope`       | No scope requested, a scope isn’t supported, or a scope isn’t in the client’s registered `scopes_allowed`. |
| `server_error`        | Resend failed to persist the authorization request.                                                        |

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## Related pages

- [Account Management](./account-management-index.md)
- [API Keys](./api-keys-2-index.md)
- [API Keys](./api-keys-index.md)
- [API Reference](./api-reference-index.md)
- [AudiencesDEPRECATED](./audiencesdeprecated-index.md)
- [Authorized Apps](./authorized-apps-index.md)
- [Automations](./automations-index.md)
- [Broadcasts](./broadcasts-index.md)
- [Build with AI](./build-with-ai-index.md)
- [Changelog](../changelog.md)

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