Update Gateway account service Documentation for SIWA support

[p5150j]

Update Gateway account service Documentation for SIWA support

Summary:

As a technical writer, I want to update the Gateway documentation so developers can easily integrate the updated Gateway Account Service and SIWA.

Acceptance Criteria:

• Document the new methods and flows in the Gateway, including getAuthenticationSessionUrl(), processAuthorizationCode(), and processSiwaPayloadResponse().
• Update API references with request and response examples.
• Provide detailed guides on how the app backend should interact with the Gateway.
• Ensure that the documentation includes the processing of the SiwaPayloadResponse.
• Include diagrams and flowcharts matching the updated flows.
• Review and publish the updated documentation in the developer portal.

Tasks:

1. Gather information on all new and updated Gateway features.
2. Write clear and concise documentation for each method and process.
3. Update existing guides to reflect changes in the authentication flow.
4. Create visual aids (e.g., updated sequence diagrams) to help explain the flows.
5. Proofread and validate the documentation with the development team.
6. Publish the documentation and ensure it is accessible to developers.