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SAS and Token Issues

1. Summary

SAS failures usually come from time-window, permission, scope, or restriction mismatches. The token often looks valid at a glance but is invalid for the exact request being made.

mermaid flowchart TD A[SAS request fails] --> B{Time window valid?} B -->|No| C[Fix st or se and clock skew] B -->|Yes| D{Permissions and scope match?} D -->|No| E[Regenerate SAS correctly] D -->|Yes| F{Protocol or IP restriction problem?} F -->|Yes| G[Adjust restrictions]

2. Common Misreadings

  • Setting the SAS start time to the current second on skewed systems.
  • Using a service SAS where account SAS scope is required, or the reverse.
  • Forgetting that IP or protocol restrictions can silently invalidate a token.

3. Competing Hypotheses

  • H1: SAS is expired or not yet valid.
  • H2: Permission set does not match the attempted operation.
  • H3: Resource scope is wrong.
  • H4: IP or protocol restriction blocks usage.

4. What to Check First

  • st and se values in UTC.
  • Client clock skew.
  • sp permissions and resource scope.
  • sip and spr restrictions.

5. Evidence to Collect

  • Sanitized SAS field breakdown.
  • Error timestamp and client clock.
  • Requested operation and target resource path.
  • Key rotation or SAS regeneration history if relevant.

6. Validation and Disproof by Hypothesis

H1: Time-window problem

  • Support: request time falls before st or after se.
  • Weaken: same SAS works consistently inside the same time window.

H2: Permission mismatch

  • Support: token lacks required r, w, d, or list permissions.
  • Weaken: permission set clearly covers the attempted operation.

H3: Scope mismatch

  • Support: SAS created at account/container scope but used for another target type.
  • Weaken: scope exactly matches the accessed resource.

H4: Restriction mismatch

  • Support: IP or protocol settings exclude the active client path.
  • Weaken: request path and client source are within allowed limits.

7. Likely Root Cause Patterns

  • Immediate token use with no clock-skew buffer.
  • Wrong SAS type or scope.
  • Missing permission flags.
  • Hidden IP or HTTPS-only restriction mismatch.

8. Immediate Mitigations

  • Regenerate SAS with correct scope and permissions.
  • Add a safe clock-skew buffer.
  • Remove unintended IP/protocol restrictions.
  • Re-test with one sanitized known-good token.

9. Prevention

  • Centralize SAS generation logic.
  • Prefer short-lived tokens with tested templates.
  • Validate time, permission, scope, and restriction fields in automation.

See Also

Sources