ActAs令牌处理程序不用于ActAs请求

Question

我有一个自定义SecurityTokenHandler用于默认和ActAs令牌请求。问题是默认令牌处理程序是为默认和ActAs请求调用的。我应该怎么做才能将默认和ActAs令牌请求的处理程序分开？

我的SecurityTokenHandlers配置：

this.SecurityTokenHandlers.Clear();
            this.SecurityTokenHandlers.Add(new EncryptedSecurityTokenHandler());
            this.SecurityTokenHandlers.Add(new SamlSecurityTokenHandler());
            this.SecurityTokenHandlers.Add(new CustomUserNameSecurityTokenHandler("default handler"));

            SecurityTokenHandlerCollection securityTokenHandlers = new SecurityTokenHandlerCollection()
            {
                new EncryptedSecurityTokenHandler(),
                new SamlSecurityTokenHandler(),
                new CustomUserNameSecurityTokenHandler("actas handler")
            };

            SecurityTokenHandlerCollectionManager[SecurityTokenHandlerCollectionManager.Usage.ActAs] = securityTokenHandlers;

CustomUserNameSecurityTokenHandler如下：

public class CustomUserNameSecurityTokenHandler : UserNameSecurityTokenHandler
    {
        string handler;
        public CustomUserNameSecurityTokenHandler(string handler) : base()
        {
            this.handler = handler;
        }
...

WIF实例化两个类，但永远不会调用"actas handler"参数化处理程序，每次只调用"default handler"个。

这是一个示例RequestSecurityToken：

var rst = new RequestSecurityToken
            {
                RequestType = RequestTypes.Issue,
                AppliesTo = new EndpointReference(appliesTo.Uri.AbsoluteUri),
                KeyType = KeyTypes.Bearer,
                ActAs = new SecurityTokenElement(new UserNameSecurityToken("test", null))
            };

我很感激任何帮助。