Add support for proxy (#2286)

Co-authored-by: Nikola Jokic <jokicnikola07@gmail.com>
Co-authored-by: Tingluo Huang <tingluohuang@github.com>
Co-authored-by: Ferenc Hammerl <fhammerl@github.com>

github/actions/client_proxy_test.go

@@ -0,0 +1,39 @@
+package actions_test
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/actions/actions-runner-controller/github/actions/testserver"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/http/httpproxy"
+)
+
+func TestClientProxy(t *testing.T) {
+	serverCalled := false
+
+	proxy := testserver.New(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		serverCalled = true
+	}))
+
+	proxyConfig := &httpproxy.Config{
+		HTTPProxy: proxy.URL,
+	}
+	proxyFunc := func(req *http.Request) (*url.URL, error) {
+		return proxyConfig.ProxyFunc()(req.URL)
+	}
+
+	c, err := actions.NewClient("http://github.com/org/repo", nil, actions.WithProxy(proxyFunc))
+	require.NoError(t, err)
+
+	req, err := http.NewRequest(http.MethodGet, "http://example.com", nil)
+	require.NoError(t, err)
+
+	_, err = c.Do(req)
+	require.NoError(t, err)
+
+	assert.True(t, serverCalled)
+}