Add a stub for auth scheme

neofs/auth.go

@@ -0,0 +1,23 @@
+package neofs
+
+import (
+	br "github.com/google/brotli/go/cbrotli"
+	"github.com/nspcc-dev/neofs-api-go/service"
+	"github.com/pkg/errors"
+)
+
+func UnpackBearerToken(packedCredentials []byte) (service.BearerToken, error) {
+	// secretHash := packedCredentials[:32]
+	_ = packedCredentials[:32]
+	compressedKeyID := packedCredentials[32:]
+	keyID, err := br.Decode(compressedKeyID)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to decompress key ID")
+	}
+	bearerToken := new(service.BearerTokenMsg)
+	if err = bearerToken.Unmarshal(keyID); err != nil {
+		return nil, errors.Wrap(err, "failed to unmarshal embedded bearer token")
+	}
+	// TODO
+	return bearerToken, nil
+}