The token printed for authorized requests has a lifetime of 1h. If an
upload exceeds 1h, a chunk push will fail since the token is created on
a "start upload" request.
This replaces the Pipe with SectionReader which is simpler and
implements Seek, a requirement for makeRequestWithRetry. This is
slightly worse than using a Pipe since the progress update is directly
tied to the chunk size instead of controlled separately.
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