Parse the Green Button/NAESB ESPI Atom+XML feed (UsagePoint, MeterReading, IntervalBlock, IntervalReading, ReadingType) returned after a Connect My Data authorization.

Steps

1. After completing OAuth2 authorization via Connect My Data, fetch the data as an Atom Syndication Format (RFC 4287) XML document wrapping ESPI-namespaced content per the NAESB Energy Services Provider Interface (ESPI) standard.
2. Parse the top-level feed (or a single entry when only one resource is returned), iterating entries whose content holds one ESPI resource: UsagePoint, MeterReading, ReadingType, IntervalBlock, UsageSummary, LocalTimeParameters, etc.
3. Follow each entry's Atom link elements (rel=self/up/related) — these hold absolute URLs that act as identifiers linking, e.g., a MeterReading or IntervalBlock back to its parent UsagePoint.
4. Resolve the ReadingType referenced from a MeterReading before interpreting readings — it defines the unit of measure, power-of-ten multiplier, and interval duration for the associated data.
5. Extract IntervalBlock entries and their child IntervalReading elements (timestamp/duration plus raw value) as the actual usage data points, applying the ReadingType's multiplier before use.
6. Optionally validate against the espi.xsd/atom.xsd referenced in the feed's schemaLocation to catch malformed data before downstream consumption.