feat: support rest.WithCorsHeaders to customize cors headers (#4284)

rest/internal/cors/handlers.go

@@ -26,6 +26,11 @@ const (
 	originHeader     = "Origin"
 )
 
+// AddAllowHeaders sets the allowed headers.
+func AddAllowHeaders(header http.Header, headers ...string) {
+	header.Add(allowHeaders, strings.Join(headers, ", "))
+}
+
 // NotAllowedHandler handles cross domain not allowed requests.
 // At most one origin can be specified, other origins are ignored if given, default to be *.
 func NotAllowedHandler(fn func(w http.ResponseWriter), origins ...string) http.Handler {

rest/internal/cors/handlers_test.go

@@ -3,11 +3,80 @@ package cors
 import (
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
 
+func TestAddAllowHeaders(t *testing.T) {
+	tests := []struct {
+		name     string
+		initial  string
+		headers  []string
+		expected string
+	}{
+		{
+			name:     "single header",
+			initial:  "",
+			headers:  []string{"Content-Type"},
+			expected: "Content-Type",
+		},
+		{
+			name:     "multiple headers",
+			initial:  "",
+			headers:  []string{"Content-Type", "Authorization", "X-Requested-With"},
+			expected: "Content-Type, Authorization, X-Requested-With",
+		},
+		{
+			name:     "add to existing headers",
+			initial:  "Origin, Accept",
+			headers:  []string{"Content-Type"},
+			expected: "Origin, Accept, Content-Type",
+		},
+		{
+			name:     "no headers",
+			initial:  "",
+			headers:  []string{},
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			header := http.Header{}
+			headers := make(map[string]struct{})
+			if tt.initial != "" {
+				header.Set(allowHeaders, tt.initial)
+				vals := strings.Split(tt.initial, ", ")
+				for _, v := range vals {
+					headers[v] = struct{}{}
+				}
+			}
+			for _, h := range tt.headers {
+				headers[h] = struct{}{}
+			}
+			AddAllowHeaders(header, tt.headers...)
+			var actual []string
+			vals := header.Values(allowHeaders)
+			for _, v := range vals {
+				bunch := strings.Split(v, ", ")
+				for _, b := range bunch {
+					if len(b) > 0 {
+						actual = append(actual, b)
+					}
+				}
+			}
+
+			var expect []string
+			for k := range headers {
+				expect = append(expect, k)
+			}
+			assert.ElementsMatch(t, expect, actual)
+		})
+	}
+}
+
 func TestCorsHandlerWithOrigins(t *testing.T) {
 	tests := []struct {
 		name      string