Use the USPS Tracking API v3 to retrieve package events and set up proactive tracking

Steps

1. Authenticate via OAuth 2.0 by POSTing to https://apis.usps.com/oauth2/v3/token with your client credentials to get a bearer token
2. GET https://apis.usps.com/tracking/v3/tracking/{trackingNumber} with the USPS tracking number as a path parameter; include the expand=DETAIL query parameter to receive full event history
3. Parse the trackSummary and trackDetail arrays from the response for event descriptions, timestamps, and locations
4. For proactive notifications, call GET https://apis.usps.com/tracking/v3/tracking/{trackingNumber}?expand=SUMMARY&revisedDeliveryDate=true to check for estimated delivery date updates
5. Handle HTTP 404 responses gracefully: USPS tracking numbers are not activated in the system until the package's first acceptance scan, so early queries legitimately return not found
6. Implement exponential backoff when polling: USPS tracking data typically updates at scan events, not continuously