feat: support CORS by using rest.WithCors(...) (#1212)

* feat: support CORS by using rest.WithCors(...)

* chore: add comments

* refactor: lowercase unexported methods

* ci: fix lint errors

rest/internal/cors/handlers_test.go

@@ -0,0 +1,76 @@
+package cors
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCorsHandlerWithOrigins(t *testing.T) {
+	tests := []struct {
+		name    string
+		origins []string
+		expect  string
+	}{
+		{
+			name:   "allow all origins",
+			expect: allOrigins,
+		},
+		{
+			name:    "allow one origin",
+			origins: []string{"local"},
+			expect:  "local",
+		},
+		{
+			name:    "allow many origins",
+			origins: []string{"local", "remote"},
+			expect:  "local",
+		},
+	}
+
+	methods := []string{
+		http.MethodOptions,
+		http.MethodGet,
+		http.MethodPost,
+	}
+
+	for _, test := range tests {
+		for _, method := range methods {
+			test := test
+			t.Run(test.name+"-handler", func(t *testing.T) {
+				r := httptest.NewRequest(method, "http://localhost", nil)
+				w := httptest.NewRecorder()
+				handler := Handler(test.origins...)
+				handler.ServeHTTP(w, r)
+				if method == http.MethodOptions {
+					assert.Equal(t, http.StatusNoContent, w.Result().StatusCode)
+				} else {
+					assert.Equal(t, http.StatusNotFound, w.Result().StatusCode)
+				}
+				assert.Equal(t, test.expect, w.Header().Get(allowOrigin))
+			})
+		}
+	}
+
+	for _, test := range tests {
+		for _, method := range methods {
+			test := test
+			t.Run(test.name+"-middleware", func(t *testing.T) {
+				r := httptest.NewRequest(method, "http://localhost", nil)
+				w := httptest.NewRecorder()
+				handler := Middleware(test.origins...)(func(w http.ResponseWriter, r *http.Request) {
+					w.WriteHeader(http.StatusOK)
+				})
+				handler.ServeHTTP(w, r)
+				if method == http.MethodOptions {
+					assert.Equal(t, http.StatusNoContent, w.Result().StatusCode)
+				} else {
+					assert.Equal(t, http.StatusOK, w.Result().StatusCode)
+				}
+				assert.Equal(t, test.expect, w.Header().Get(allowOrigin))
+			})
+		}
+	}
+}