Troubleshooting OAuth Authentication Failures with Splunk SOAR HTTP App

Applicability

Description

When using the Splunk SOAR HTTP app to authenticate against an OAuth-based API, the default implementation may send credentials within the request body (e.g., client_credentials). Certain third-party APIs require the client_id and client_secret to be passed as a Base64-encoded Authorization: Basic header. If the API endpoint expects this header and does not receive it, it will return an HTTP 403 Forbidden error, preventing successful connectivity.

Investigation

1. Navigate to the Test Connectivity output within the affected asset.
2. Confirm the error returned is an HTTP 403 Forbidden specifically during the token acquisition phase.
3. Consult the third-party API documentation to determine if the OAuth token endpoint mandates a Basic authentication header with Base64-encoded credentials.
4. Compare the expected request format from the API documentation with the payload being sent by the HTTP app.

Resolution

To resolve this issue, one of the following methods should be utilized:

1. Alternative Authentication Method: If the third-party API supports it, configure the HTTP app to use Basic Authentication (username and password) or a non-expiring API token directly, bypassing the OAuth flow.
2. Custom App Development: Clone the existing HTTP app and modify the underlying Python code to include the Authorization header containing the Base64-encoded client credentials.
3. Custom Function: Develop a custom function within the Splunk SOAR playbook environment using the requests library to handle the OAuth token request. This allows for full control over the headers and payload construction required by the third-party API.