- **Description:**
- Fix#12870: set scope in `default` func (ref:
https://google-auth.readthedocs.io/en/master/reference/google.auth.html)
- Moved the code to load default credentials to the bottom for clarity
of the logic
- Add docstring and comment for each credential loading logic
- **Issue:** https://github.com/langchain-ai/langchain/issues/12870
- **Dependencies:** no dependencies change
- **Tag maintainer:** for a quicker response, tag the relevant
maintainer (see below),
- **Twitter handle:** @gymnstcs
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Co-authored-by: Chester Curme <chester.curme@gmail.com>
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