Is there an automated way of get OAuth User Access token

Question

Answer

No, there is no way to generate the authorization code grant token without getting user consent. You need to get the consent from the user at least once as you cannot generate a user access token without getting the user consent.

For more comprehensive information, please refer to this API documentation: https://developer.ebay.com/api-docs/static/oauth-auth-code-grant-request.html 

Authorization code grant process returns a refresh_token which is a long-lived value that you can use to update an expired User access token. This means you do not have to get the user's consent each time you need a new User access token. You can store this refresh_token and you can update an expired User access token.

For in-depth insights, refer to the Refresh Token API documentation: https://developer.ebay.com/api-docs/static/oauth-refresh-token-request.html 

Additional Resource

OAuth best practices: https://developer.ebay.com/api-docs/static/oauth-best-practices.html