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Machine ID: Warn when returned cert TTL is less than expected #52833

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merged 3 commits into from
Mar 12, 2025
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Machine ID: Warn when returned cert TTL is less than expected #52833

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2ddb748
Machine ID: Warn when returned cert TTL is less than expected
timothyb89 Mar 6, 2025
ec2bd58
Add warning on most outputs; add TODO comment for future improvements
timothyb89 Mar 11, 2025
db69ac3
Mute slonglint false positivess
timothyb89 Mar 11, 2025
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41 changes: 41 additions & 0 deletions lib/tbot/output_utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -396,6 +396,47 @@ func generateIdentity(
return newIdentity, nil
}

// warnOnEarlyExpiration logs a warning if the given identity is likely to
// expire problematically early. This can happen if either the configured TTL is
// less than the renewal interval, or if the server returns certs valid for a
// shorter-than-expected period of time.
// This assumes the identity was just renewed, for the purposes of calculating
// TTLs.
func warnOnEarlyExpiration(
ctx context.Context,
log *slog.Logger,
ident *identity.Identity,
lifetime config.CredentialLifetime,
) {
// Calculate a rough TTL, assuming this was called shortly after the
// identity was returned. We'll add a minute buffer to compensate and avoid
// superfluous warning messages.
effectiveTTL := ident.TLSIdentity.Expires.Sub(time.Now()) + time.Minute

if effectiveTTL < lifetime.TTL {
l := log.With(
"requested_ttl", lifetime.TTL,
"renewal_interval", lifetime.RenewalInterval,
"effective_ttl", effectiveTTL,
"expires", ident.TLSIdentity.Expires,
"roles", ident.TLSIdentity.Groups,
)

if effectiveTTL < lifetime.RenewalInterval {
l.WarnContext(ctx, "The server returned an identity shorter than "+
"expected and below the configured renewal interval, probably "+
"due to a `max_session_ttl` configured on a server-side role. "+
"Unless corrected, the credentials will be invalid for some "+
"period until renewal.")
} else {
l.WarnContext(ctx, "The server returned an identity shorter than "+
"the requested TTL, probably due to a `max_session_ttl` "+
"configured on a server-side role. It may not remain valid as "+
"long as expected.")
Comment on lines +439 to +442
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I did some experimenting and found that bots can always fetch their own roles, so technically we could make some queries and log exactly which role caused the shortened TTL. Any thoughts on whether or not that would be worth the effort?

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That'd be a really nice touch, but I think it depends on how many roles bots have in the common case. My hunch is that it's low enough that it wouldn't take users long to figure out which is the problematic role.

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Yeah, and adds network calls on what's already a semi-error path, which isn't ideal. I think I'll stick with the simpler implementation for now, and maybe add a note to indicate we could improve this in the future if we see users having trouble.

}
}
}

// fetchDefaultRoles requests the bot's own role from the auth server and
// extracts its full list of allowed roles.
func fetchDefaultRoles(ctx context.Context, roleGetter services.RoleGetter, identity *identity.Identity) ([]string, error) {
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2 changes: 2 additions & 0 deletions lib/tbot/service_identity_output.go
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Original file line number Diff line number Diff line change
Expand Up @@ -152,6 +152,8 @@ func (s *IdentityOutputService) generate(ctx context.Context) error {
}
}

warnOnEarlyExpiration(ctx, s.log.With("output", s), id, cmp.Or(s.cfg.CredentialLifetime, s.botCfg.CredentialLifetime))

hostCAs, err := s.botAuthClient.GetCertAuthorities(ctx, types.HostCA, false)
if err != nil {
return trace.Wrap(err)
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