connect accounts and pull transactions via the MX Platform API

Steps

1. Obtain API keys (client_id and api_key) from the MX developer portal and authenticate all requests using HTTP Basic auth with client_id as the username and api_key as the password.
2. Create a user for each end user in your system by POSTing to /users with an optional external identifier; receive the user's guid.
3. Generate a widget URL for the MX Connect widget by POSTing to /users/{user_guid}/widget_urls with widget_type=connect_widget; embed this URL in an iframe or webview in your application.
4. Handle the postMessage or callback from the Connect widget on successful account linking to receive the member_guid of the newly connected institution member.
5. Retrieve accounts by calling GET /users/{user_guid}/members/{member_guid}/accounts; each account has a guid used for subsequent data calls.
6. Fetch transactions by calling GET /users/{user_guid}/transactions with optional date range filters (from_date, to_date) and pagination parameters (page, records_per_page).