added docs

Signed-off-by: mqf20 <mingqingfoo@gmail.com>

credential/access_token.go

@@ -7,10 +7,12 @@ type AccessTokenHandle interface {
 	GetAccessToken() (accessToken string, err error)
 }
 
+// AccessTokenCompatibleHandle 允许 AccessTokenHandle 兼容 AccessTokenContextHandle.
 type AccessTokenCompatibleHandle struct {
 	AccessTokenHandle
 }
 
+// GetAccessTokenContext 获取access_token,先从cache中获取，没有则从服务端获取
 func (c AccessTokenCompatibleHandle) GetAccessTokenContext(_ context.Context) (accessToken string, err error) {
 	return c.GetAccessToken()
 }