if len(signedHdrFields) != 2 {
		return nil, ErrMissingFields
	}
	if signedHdrFields[0] != "SignedHeaders" {
		return nil, ErrMissingSignHeadersTag
	}
	if signedHdrFields[1] == "" {
		return nil, ErrMissingFields
	}
	signedHeaders := strings.Split(signedHdrFields[1], ";")
	return signedHeaders, ErrNone
}

// signValues data type represents structured form of AWS Signature V4 header.

// extractSignedHeaders extract signed headers from Authorization header
func extractSignedHeaders(signedHeaders []string, r *http.Request) (http.Header, APIErrorCode) {
	reqHeaders := r.Header
	reqQueries := r.Form
	// find whether "host" is part of list of signed headers.
	// if not return ErrUnsignedHeaders. "host" is mandatory.
	if !slices.Contains(signedHeaders, "host") {
		return nil, ErrUnsignedHeaders
	}

    "groups": null,
    "action": "s3:ListBucket",
    "bucket": "test",
    "conditions": {
      "Authorization": [
        "AWS4-HMAC-SHA256 Credential=minio/20220507/us-east-1/s3/aws4_request, SignedHeaders=host;x-amz-content-sha256;x-amz-date, Signature=62012db6c47d697620cf6c68f0f45f6e34894589a53ab1faf6dc94338468c78a"
      ],
      "CurrentTime": [
        "2022-05-07T18:31:41Z"
      ],
      "Delimiter": [
        "/"

curl -v $(go run presigned.go)
...
...
> GET /functionbucket/testobject?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=minioadmin%2F20230205%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20230205T173023Z&X-Amz-Expires=1000&X-Amz-SignedHeaders=host&lambdaArn=arn%3Aminio%3As3-object-lambda%3A%3Atoupper%3Awebhook&X-Amz-Signature=d7e343f0da9d4fa2bc822c12ad2f54300ff16796a1edaa6d31f1313c8e94d5b2 HTTP/1.1
> Host: localhost:9000
> User-Agent: curl/7.81.0
> Accept: */*