Fixed desired directory structure.

google/internal/externalaccount/oauth/clientAuthentication.go

@@ -0,0 +1,39 @@
+package externalaccount
+
+import (
+	"encoding/base64"
+	"golang.org/x/oauth2"
+	"net/http"
+	"net/url"
+)
+
+// ClientAuthentication represents an OAuth client ID and secret and the mechanism for passing these credentials as stated in rfc6749#2.3.1
+type ClientAuthentication struct {
+	//Can be either basic or request-body
+	AuthStyle    oauth2.AuthStyle
+	ClientID     string
+	ClientSecret string
+}
+
+func (c *ClientAuthentication) InjectAuthentication(values *url.Values, headers *http.Header) {
+	if c.ClientID == "" || c.ClientSecret == "" || values == nil || headers == nil {
+		return
+	}
+
+	switch c.AuthStyle {
+	case oauth2.AuthStyleInHeader:
+		plainHeader := c.ClientID + ":" + c.ClientSecret
+		headers.Add("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(plainHeader)))
+	case oauth2.AuthStyleInParams:
+		values.Set("client_id", c.ClientID)
+		values.Set("client_secret", c.ClientSecret)
+	case oauth2.AuthStyleAutoDetect:
+		values.Set("client_id", c.ClientID)
+		values.Set("client_secret", c.ClientSecret)
+	default:
+		values.Set("client_id", c.ClientID)
+		values.Set("client_secret", c.ClientSecret)
+	}
+
+	return
+}