GetDiscoveryDocumentAsync 失败，IdentityServer4 客户端

Question

I have a helper class to get access token from IdentityServer4. Here is the code:

public class ServerTokenHelper
{
    static TokenResponse Token { get; set; }
    static DateTime ExpiryTime { get; set; }

    string  _host;
    string _clientId;
    string _clientSecret;
    string _clientScopes;

    static object ThreadLock = new object();


    static ConcurrentDictionary<string, Tuple<string, string, TokenResponse, DateTime>> userNameCache =
        new ConcurrentDictionary<string, Tuple<string, string, TokenResponse, DateTime>>();
    private static HttpClient _tokenClient = new HttpClient();

    public ServerTokenHelper(string commAddress, string host, string clientId, string clientSecret, string clientScopes)
    {
        _host = host;
        _clientId = clientId;
        _clientSecret = clientSecret;
        _clientScopes = clientScopes;
    }
        public async Task<TokenResponse> GetUserTokenResponseAsync(string userName, string password)
    {
        if (userName != null && userName.Length > 0)
        {
            lock (ThreadLock)
            {
                if (userNameCache.TryGetValue(userName, out var cacheItem))
                {
                    // Since we always cache the result below, we should verify before reusing an entry that the IdentityToken
                    // isn't null because of an error getting it last time!
                    if (cacheItem.Item2 == password && cacheItem.Item3 != null && cacheItem.Item3.IdentityToken != null
                        && cacheItem.Item4 > DateTime.UtcNow)
                    {
                        // System.Diagnostics.Debug.WriteLine($"GetUserTokenResponseAsync({userName}): returning cached value");
                        return cacheItem.Item3;
                    }
                }
            }
        }

        Trace.WriteLine($"GetUserTokenResponseAsync({userName}): new token being retrieved...");

        bool blHttps = false;
        if (_host.ToLower().Contains("https")) blHttps = true;
        var disco = await _tokenClient.GetDiscoveryDocumentAsync(new DiscoveryDocumentRequest
        {
            Address = _host,
            Policy = { RequireHttps = blHttps }
        });
        if (disco.IsError)
        {
            Trace.WriteLine($"GetUserTokenResponseAsync({userName}): GetDiscoveryDocumentAsync failed: {disco.Error}");
            return null;
        }
        // request token
        var tokenResponse = await _tokenClient.RequestPasswordTokenAsync(new PasswordTokenRequest
        {
            Address = disco.TokenEndpoint,
            ClientId = _clientId,
            ClientSecret = _clientSecret,
            Scope = _clientScopes,
            UserName = userName,
            Password = password
        });
        if (tokenResponse.IsError)
        {
            Trace.WriteLine($"GetUserTokenResponseAsync({userName}): Could not retrieve token. {tokenResponse.Error} - {tokenResponse.ErrorDescription}");
        }

        lock (ThreadLock)
        {
            userNameCache[userName] = Tuple.Create(userName, password, tokenResponse,
                DateTime.UtcNow.AddSeconds((tokenResponse != null) ? tokenResponse.ExpiresIn - 120 : 0));
        }

        return tokenResponse;
    }

} The intent of above codes is to get access token for User Resources Password flow. Recently, someone changed from

private HttpClient _tokenClient = new HttpClient();

to

private static HttpClient _tokenClient = new HttpClient();

With this change, we got some errors occasionally. The code function is in production server. There may be several thousands of api calls each hour. Here is the error message:

GetUserTokenResponseAsync: GetDiscoveryDocumentAsync failed

Can someone explain what is the issue caused by this simple change?

Answer 1

With HttpClient this line is the problem

private static HttpClient _tokenClient = new HttpClient();

HttpClient is not supposed to be reused/cached, instead you are supposed to dispose it after each use, because you might otherwise get various issued, like DNS or that you run out of TCP/IP ports.

But even better, why not cache the discovery document for X minutes? That document does not change that often.

See these articles:

• You're using HttpClient wrong and it is destabilizing your software
• Use IHttpClientFactory to implement resilient HTTP requests