Add utility to read OAuth 2 token from file

[atc0005]

Overview

Provide a small CLI tool that can read an OAuth 2 token from a specified file. The idea is that another tool would be called via cron periodically to obtain an initial token or replace an existing one and that this one would read that token and emit it via stdout.

The assumption is that the input file would be in JSON format containing all relevant fields from an OAuth 2 token.

As a potential later enhancement, the tool could add support for parsing a plain text file in order to perform cleanup (e.g., removing any stray single or double quotes).

Input JSON format

For reference, here is a curl command used to fetch a token:

curl https://login.microsoftonline.com/TENAT_ID_HERE/oauth2/v2.0/token -X POST -H "Content-type: application/x-www-form-urlencoded" -d "client_id=CLIENT_ID_HERE&scope=https%3A%2F%2Foutlook.office365.com%2F.default&grant_type=client_credentials&username=me@example.com&client_secret=CLIENT_SECRET_HERE"

and the "pretty printed" JSON response:

{
    "token_type": "Bearer",
    "expires_in": 3599,
    "ext_expires_in": 3599,
    "access_token": "TOKEN_HERE"
}

References

• Research: OATH2 support for accessing O365 mailboxes via IMAP #313
• Add utility to obtain OAuth 2 token via Client Credentials flow #319

[atc0005]

The JSON response doesn't indicate a specific time, but rather a duration. We know from the time the token was received that we have approximately 3599 seconds remaining before the token is invalid. How we track that time is an implementation detail.

One way that comes to mind is a field in a SQLite database table, but a simpler approach is likely to be a mod date/time on a written file. Read the metadata of an input JSON file and refuse to proceed further if the token is determined to be expired.