### AWS IAM authentication

The security updates added in Vault 1.5.1, 1.4.4, 1.3.8, and 1.2.5 include additional header checking
during AWS IAM authentication. The default list of allowed headers doesn't include some that are
commonly present, which may result in a login error of the form:

```
Cannot login using AWS-IAM: invalid request header: X-Amz-Security-Token
```

This issue affects 1.5.2, 1.4.5, 1.3.9, and 1.2.6 as well. It has been corrected in 1.5.3, 1.4.6,
1.3.10 and 1.2.7. The affected released versions can work around the issue by manually configuring
the allowed header list, including all needed headers. A recommended configuration is shown below:

```
vault write auth/aws/config/client \
   allowed_sts_header_values="Content-Type" \
   allowed_sts_header_values="Content-Length" \
   allowed_sts_header_values="User-Agent" \
   allowed_sts_header_values="X-Amz-Date" \
   allowed_sts_header_values="Authorization" \
   allowed_sts_header_values="X-Amz-Security-Token" \
   allowed_sts_header_values="Host" \
   allowed_sts_header_values="X-Vault-Aws-Iam-Server-Id"
```
