# Azure Storage: Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature (AuthenticationFailed)

**Code:** `AuthenticationFailed` · **Category:** Azure · **Seen on:** Azure

The storage request’s signature or SAS token is invalid — wrong/rotated account key, expired SAS, or clock skew.

## Meaning

Shared Key and SAS signatures depend on the key, the exact request and the time. Rotated keys, SAS tokens outside their start/expiry window, mangled URL encoding, or a machine clock off by more than 15 minutes all fail.

## Common causes

- Account key rotated/old connection string
- SAS expired or start time in the future
- SAS URL-encoding broken (+ or %2B)
- System clock skew
- Signed resource/permissions don’t match the operation

## Quick fix

1. Regenerate the connection string/SAS from current keys
2. Set SAS start time a few minutes in the past
3. Sync the system clock

## Detailed fix by platform

### Azure CLI

1. 

```bash
az storage account keys list -n stapp -g rg --query "[0].value" -o tsv
az storage container generate-sas --account-name stapp -n data --permissions rl --expiry 2026-12-31T00:00Z --auth-mode login --as-user
```


## How to diagnose

1. **Detail** — AuthenticationErrorDetail text
2. **Times** — SAS st/se vs current UTC
3. **Key** — Which key was used?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/azure/storage-authenticationfailed)