fix: fix token clock skew issue #333
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anubhav756
previously approved these changes
Aug 8, 2025
kurtisvg
reviewed
Aug 11, 2025
| @@ -71,7 +71,9 @@ def _update_cache(new_token: str) -> None: | |||
| # verify_oauth2_token not only decodes but also validates the token's | |||
| # signature and claims against Google's public keys. | |||
| # It's a synchronous, CPU-bound operation, safe for async contexts. | |||
| claims = id_token.verify_oauth2_token(new_token, Request()) | |||
| claims = id_token.verify_oauth2_token( | |||
| new_token, Request(), clock_skew_in_seconds=60 | |||
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60s is a long time. Would we be better off with a smaller range of like 1s or 5s?
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I didn't find any standard implementations of this. I did, however, see that firebase only allows clock_skew < 60 (ref).
I have changed it to 10 for now. Let me know if you think that's too much and we should make it smaller.
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Token used too early errors are a known issue.
For example: firebase/firebase-admin-python#624, googleapis/google-auth-library-python#889
This happens when the system clock is not completely syncronised with the server. The function
verify_id_tokenmay fail for tokens that were issued by servers which have clocks running a little early.If verification is done right after the token was issued by such a server, then the call to function
google.oauth2.id_token.verify_tokenmay be early enough for the 'issued-at-time' timestamp of the token still being in the future.Adding the optional parameter
clock_skew_in_seconds=60to the call togoogle.oauth2.id_token.verify_tokenwould allow for the servers clock to be off by up to a minute and still allow verification of the issued token immediately after it being issued.Fixes #332