This PR introduces two new features
- AWS STS compatible STS API named AssumeRoleWithClientGrants
```
POST /?Action=AssumeRoleWithClientGrants&Token=<jwt>
```
This API endpoint returns temporary access credentials, access
tokens signature types supported by this API
- RSA keys
- ECDSA keys
Fetches the required public key from the JWKS endpoints, provides
them as rsa or ecdsa public keys.
- External policy engine support, in this case OPA policy engine
- Credentials are stored on disks
This commit fixes an AWS S3 incompatibility issue.
The AccessKeyID may contain one or more `/` which caused
the server to interpret parts of the AccessKeyID as
other `X-Amz-Credential` parameters (like date, region, ...)
This commit fixes this by allowing 5 or more
`X-Amz-Credential` parameter strings and only interpreting
the last 5.
Fixes#6443
