# Create an application credential

`POST /v1/applications/{application_id}/credentials` · permission `applications:write` · optional `Idempotency-Key`

Adds a credential to an application: a platform-generated client secret (`type: client_secret`) or a registered public key for `private_key_jwt` (`type: public_key`).

- **Client secret.** The response carries `client_secret` once. It cannot be retrieved again; store it immediately. An application holds at most 2 active secrets, so a secret can be rotated without downtime.
- **Public key.** Send the public JWK in `jwk`. A JWK with private members (`d`, `p`, `q`, `dp`, `dq`, `qi`, `oth`, `k`) or larger than 16 KiB is rejected. An application holds at most 5 keys.
- **Idempotent replay.** Repeating the request with the same `Idempotency-Key` replays the stored response without the secret: the body has `secret_redacted: true` and no `client_secret`. Create a new credential if the secret was lost.

## Request

| Parameter | In | Description |
|---|---|---|
| `application_id` | path | Application id (`app_…`). |

Body:

| Field | Type | Description |
|---|---|---|
| `type` | string | Required. `client_secret` or `public_key`. |
| `expires_at` | string (date-time) | Optional, `client_secret` only; must be in the future. |
| `jwk` | object | Required for `public_key`; a public JWK, at most 16 KiB. |

## Response

`201 Created` with `Cache-Control: no-store`. The credential object as in the list response; for `client_secret` it also has `client_secret`.

```json
{
  "id": "cred_0000000000000000000000001z",
  "type": "client_secret",
  "secret_last4": "abcd",
  "client_secret": "<shown once>",
  "expires_at": null
}
```

## Errors

| HTTP | `code` | When |
|---|---|---|
| 401 | `unauthenticated` | The key is missing, invalid or revoked. |
| 403 | `insufficient_permissions` | The key lacks the required permission. |
| 404 | `not_found` | The application does not exist in this environment. |
| 409 | `credential_limit_reached` | The application already has the maximum number of active secrets (2) or keys (5). |
| 409 | `conflict` | The same public key is already registered for the application. |
| 422 | `validation_failed` | The body is invalid: unknown `type`, missing `jwk`, private JWK members, JWK too large, `expires_at` in the past or sent with `public_key`, or a credential type the application type does not allow (`/type: not_allowed`: `client_secret` only for `web` and `m2m`; `public_key` for `web`, `m2m`, `device` and `management`; `spa` and `native` are public clients and take no credentials). |
| 503 | `service_unavailable` | The credential registry is temporarily unavailable; retry after the `Retry-After` delay. |

## Example

```bash
curl -X POST https://api.eu.keenauth.com/v1/applications/app_6f8d0cjgbmf0gtn2rg6pscp3cg/credentials \
  -H "Authorization: Bearer $KEENAUTH_SECRET_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"type":"client_secret"}'
```