Using Cognito Developer Identities on API Gateway JWT Authorizer

Question

In the Api Gateway JWT Authorizer, Why it is not possible to use the JWT token generated by `getOpenIdTokenForDeveloperIdentity`?:

I generate a developer identity token this way:
```js
cognitoIdentity
      .getOpenIdTokenForDeveloperIdentity({
        IdentityPoolId: "us-east-1:43d2cbc6-...",
        // null when you want to create a new identity. An existing authenticated/unauthenticated identity when you want to associate a new login with an existing IdentityId
        // IdentityId: "",
        Logins: {
          mycustomprovider: "user id in my custom provider"
        },
 })
```

It returns a JWT with a payload and header like this:
```json
{
  "sub": "us-east-1:...",
  "aud": "us-east-1:...",
  "amr": [
    "authenticated",
    "mycustomprovider",
    "mycustomprovider-east-1:...."
  ],
  "iss": "https://cognito-identity.amazonaws.com",
  "exp": 1686581019,
  "iat": 1686577419
}
```

header:
```json
{
  "kid": "us-east-13",
  "typ": "JWS",
  "alg": "RS512"
}
```

I configured a JWT Authorizer with
* Issuer: https://cognito-identity.amazonaws.com
* Audience: (value from jwt aud field) us-east-1:...

However I get this response header with a error message:
www-authenticate: Bearer scope="" error="invalid_token" error_description="unable to decode "n" from RSA public key"
status: 401 Unauthorized

What's is wrong with my configuration?

JimmyDqv · Answer

I don't think what you are trying to do is possible. The error indicate that the built in JWT authorizer can't read the public key. Normally it tries to fetch the keys from `https:///.well-known/jwks.json` however the keys for `https://cognito-identity.amazonaws.com` is different per region, tryin to fetch ` https://cognito-identity.amazonaws.com/.well-known/jwks.json` result in an access denied.

Instead try and verify using your own custom authorizer using the normal JWT validation steps.

```
1: Get OpenId config from: https://cognito-identity.amazonaws.com/.well-known/openid-configuration
2: Use the jwks_uri to fetch list of keys (e.g https://cognito-identity.amazonaws.com/.well-known/jwks_uri)
3: Use kid in token to get the correct key
4: Perform validation
```

Using Cognito Developer Identities on API Gateway JWT Authorizer

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