React BTP app throwing 403 token validation failed when teying post to backend

[sakshi7687658]

Hi,

I have a BTP react app which fetches data correctly from S4 backend through the approuter using destination. However when trying to do a post call, it needs a csrf token which it fetches correctly and passes to the Odata call correctly. However it fails giving with 403, token validation failed.

as recommended on another post, I maintained csrfprortection as false in xs-app.json as csrf token validation in my case is maintained by the backend only. 

is there any other config I need to look into, maybe in the destination setvice in mta or the actual destination in BTP, or the destination user role? 

[thomas201tang]

The 403 Forbidden error during your React app's POST call from BTP to S/4 is likely due to an issue with the session, not the token itself. While you've correctly disabled approuter CSRF protection, the backend still requires a valid session to validate the token. Check your browser's network tab to confirm that the Set-Cookie header from the initial token fetch is being sent back as a Cookie header with your POST request. Ensure your frontend fetch logic includes credentials: 'include' to handle cookies. Also, verify that the destination Nelnet user in BTP has the correct permissions for the POST operation in the S/4 backend, as this can also lead to a generic 403 error.

[sakshi7687658]

Thank you for you reply. Yes I am already doing that too, credentials have include and I’m using same destination from local environment to post and it works absolutely fine.

[sakshi7687658]

To add to that, I noticed that the cookie returned set from local has SAP SESSION ID while from CF it is vcap session id. I’m not sure if that is causing issue and how to resolve it.

[Uni_BidishaTripathi]

A 403 Forbidden error in an SAP BTP POST call means the request was understood by the server, but the client (your Fiori or BTP application or a tool like Postman) lacks the necessary authentication or authorization to access the resource.

This can be A common security measure for POST, PUT, and DELETE requests in SAP systems is CSRF protection. The server requires a special token to prevent cross-site request forgery attacks.

Symptom: Your GET request works, but the POST request fails with a 403 error.

Cause: You're not including the x-csrf-token header in your POST request.

Solution: You must first make a GET request to the same endpoint with the header x-csrf-token: Fetch. The server will respond with the token in the response header. You then include this token in the header of your subsequent POST request.

[Uni_BidishaTripathi]

The difference in session cookies between your local environment and the Cloud Foundry (CF) environment on SAP BTP is expected behavior and is unlikely to be the direct cause of a 403 Forbidden error. The issue is almost certainly due to authorization or CSRF token handling, not the session ID itself.