pstuifzand/ekster

package websub

import (
    "crypto/hmac"
    "crypto/sha1"
    "encoding/hex"
    "fmt"
    "strings"

    "github.com/pkg/errors"
)

// ValidateHubSignature validate a sha1 signature that could be send with the
// hub as an extra header
func ValidateHubSignature(sig string, feedContent, secret []byte) error {
    parts := strings.Split(sig, "=")

    if len(parts) != 2 {
        return errors.New("signature format is not like sha1=signature")
    }

    if parts[0] != "sha1" {
        return errors.New("signature format is not like sha1=signature")
    }

    // verification
    mac := hmac.New(sha1.New, secret)
    mac.Write(feedContent)
    signature := mac.Sum(nil)

    signature2, err := hex.DecodeString(parts[1])
    if err != nil {
        return errors.Wrap(err, "could not decode signature")
    }

    if !hmac.Equal(signature, signature2) {
        return fmt.Errorf("signature does not match feed %s %s", signature, parts[1])
    }

    return nil
}