Using oauth for a simple command line script to access Google's data

I recently needed to write a simple script to pull some data
from a Google website. Since I was grabbing some private data, I
needed authorize myself to do that. I found it much more work than
I expected, not because it's hard, but because there wasn't much
documentation there to guide me - I had to puzzle out what path
to go based on lots of not particularly relevant documentation. So
once I'd figured it out I decided to write a short account of what
I'd done, partly in case I need to do this again, and partly to
help anyone else who wants to do this.

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