You can use a custom OAuth app to authenticate a service account or a user account.

Create an OAuth App for User Account Authentication

Follow the procedure below to register an app and obtain the OAuthClientId and OAuthClientSecret.

Create a Custom OAuth App

1. Log into the Selling Partner Console and open Develop Apps from Apps & Services.

2. Click Add new app client.

3. Provide name for the app and select SP-API as the API type.

4. Provide IAM ARN for the AWS account and Select Sellers.

5. Provide OAuth Login URI and OAuth Redirect URI values. After creating the app, the OAuthClientId and OAuthClientSecret are displayed under LWA credentials.

For a more in depth reading of how to create a custom OAuth app and configure the IAM role, please see the Amazon Selling Partner Guide.