feat(config): support HTTP headers across providers

internal/util/header_helpers.go

@@ -0,0 +1,52 @@
+package util
+
+import (
+	"net/http"
+	"strings"
+)
+
+// ApplyCustomHeadersFromAttrs applies user-defined headers stored in the provided attributes map.
+// Custom headers override built-in defaults when conflicts occur.
+func ApplyCustomHeadersFromAttrs(r *http.Request, attrs map[string]string) {
+	if r == nil {
+		return
+	}
+	applyCustomHeaders(r, extractCustomHeaders(attrs))
+}
+
+func extractCustomHeaders(attrs map[string]string) map[string]string {
+	if len(attrs) == 0 {
+		return nil
+	}
+	headers := make(map[string]string)
+	for k, v := range attrs {
+		if !strings.HasPrefix(k, "header:") {
+			continue
+		}
+		name := strings.TrimSpace(strings.TrimPrefix(k, "header:"))
+		if name == "" {
+			continue
+		}
+		val := strings.TrimSpace(v)
+		if val == "" {
+			continue
+		}
+		headers[name] = val
+	}
+	if len(headers) == 0 {
+		return nil
+	}
+	return headers
+}
+
+func applyCustomHeaders(r *http.Request, headers map[string]string) {
+	if r == nil || len(headers) == 0 {
+		return
+	}
+	for k, v := range headers {
+		if k == "" || v == "" {
+			continue
+		}
+		r.Header.Set(k, v)
+	}
+}