Make Authenticate issue an HTTP request
diff --git a/context.go b/context.go
index 0a73890..a35242c 100644
--- a/context.go
+++ b/context.go
@@ -1,11 +1,24 @@
 package gophercloud
 
+import (
+	"net/http"
+)
+
 type Context struct {
+	// providerMap serves as a directory of supported providers.
 	providerMap map[string]*Provider
+
+	// httpClient refers to the current HTTP client interface to use.
+	httpClient *http.Client
 }
 
 func TestContext() *Context {
 	return &Context{
 		providerMap: make(map[string]*Provider),
+		httpClient: &http.Client{},
 	}
 }
+
+func (c *Context) UseCustomClient(hc *http.Client) {
+	c.httpClient = hc;
+}