Initial QSfera import

Server/vendor/github.com/lestrrat-go/jwx/v3/jws/headers.go

@@ -0,0 +1,52 @@
+package jws
+
+import (
+	"fmt"
+)
+
+func (h *stdHeaders) Copy(dst Headers) error {
+	for _, k := range h.Keys() {
+		var v any
+		if err := h.Get(k, &v); err != nil {
+			return fmt.Errorf(`failed to get header %q: %w`, k, err)
+		}
+		if err := dst.Set(k, v); err != nil {
+			return fmt.Errorf(`failed to set header %q: %w`, k, err)
+		}
+	}
+	return nil
+}
+
+// mergeHeaders merges two headers, and works even if the first Header
+// object is nil. This is not exported because ATM it felt like this
+// function is not frequently used, and MergeHeaders seemed a clunky name
+func mergeHeaders(h1, h2 Headers) (Headers, error) {
+	h3 := NewHeaders()
+
+	if h1 != nil {
+		if err := h1.Copy(h3); err != nil {
+			return nil, fmt.Errorf(`failed to copy headers from first Header: %w`, err)
+		}
+	}
+
+	if h2 != nil {
+		if err := h2.Copy(h3); err != nil {
+			return nil, fmt.Errorf(`failed to copy headers from second Header: %w`, err)
+		}
+	}
+
+	return h3, nil
+}
+
+func (h *stdHeaders) Merge(h2 Headers) (Headers, error) {
+	return mergeHeaders(h, h2)
+}
+
+// Clone creates a deep copy of the header
+func (h *stdHeaders) Clone() (Headers, error) {
+	dst := NewHeaders()
+	if err := h.Copy(dst); err != nil {
+		return nil, fmt.Errorf(`failed to copy header: %w`, err)
+	}
+	return dst, nil
+}