Add redirect and env proxy support to docker login

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)

docs/auth.go

@@ -5,12 +5,13 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"github.com/dotcloud/docker/utils"
 	"io/ioutil"
 	"net/http"
 	"os"
 	"path"
 	"strings"
+
+	"github.com/dotcloud/docker/utils"
 )
 
 // Where we store the config file
@@ -155,7 +156,13 @@ func Login(authConfig *AuthConfig, factory *utils.HTTPRequestFactory) (string, e
 		status  string
 		reqBody []byte
 		err     error
-		client        = &http.Client{}
+		client  = &http.Client{
+			Transport: &http.Transport{
+				DisableKeepAlives: true,
+				Proxy:             http.ProxyFromEnvironment,
+			},
+			CheckRedirect: AddRequiredHeadersToRedirectedRequests,
+		}
 		reqStatusCode = 0
 		serverAddress = authConfig.ServerAddress
 	)