Issue with ApacheHttpClient 4.3.3 with Microsoft TMG Proxy + HTTP Post + SSL - apache

Question

I'm having a problem with sending a POST request to Salesforce's web2lead servlet through Microsoft TMG and httpclient 4.3.3. If I try the request using Ctnlm as a proxy, it works fine (that proxies through TMG). Also, if I simply make a GET request to www.google.com through the Proxy, it's working fine. Here is the code that I'm trying to use:
HttpHost httpTargetHost = new HttpHost("www.salesforce.com", 443, "https");
HttpPost httpPost = new HttpPost("/servlet/servlet.WebToLead");
NTCredentials ntCreds = new NTCredentials("proxyUser", "proxyPassword", "workstation", "DOMAIN");
CredentialsProvider credsProvider = new BasicCredentialsProvider();
credsProvider.setCredentials(new AuthScope("proxyHost","proxyPort"), ntCreds );
HttpClientBuilder clientBuilder = HttpClientBuilder.create();
clientBuilder.useSystemProperties();
clientBuilder.setProxy(new HttpHost("proxyHost","proxyPort"));
clientBuilder.setDefaultCredentialsProvider(credsProvider);
clientBuilder.setProxyAuthenticationStrategy(new ProxyAuthenticationStrategy());
CloseableHttpClient client = clientBuilder.build();
CloseableHttpResponse response = client.execute(httpTargetHost, httpPost);
In the response, I'm getting this:
2015-01-16 17:33:31,158 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:113) - http-outgoing-0 << HTTP/1.1 407 Proxy Authentication Required ( Forefront TMG requires authorization to fulfill the request. Access to the Web Proxy filter is denied. )
2015-01-16 17:33:31,158 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Via: 1.1 PROXYHOST
2015-01-16 17:33:31,159 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Proxy-Authenticate: Negotiate
2015-01-16 17:33:31,159 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Proxy-Authenticate: Kerberos
2015-01-16 17:33:31,159 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Proxy-Authenticate: NTLM
2015-01-16 17:33:31,160 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Connection: close
2015-01-16 17:33:31,160 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Proxy-Connection: close
2015-01-16 17:33:31,160 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Pragma: no-cache
2015-01-16 17:33:31,160 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Cache-Control: no-cache
2015-01-16 17:33:31,161 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Content-Type: text/html
2015-01-16 17:33:31,161 [main] DEBUG org.apache.http.headers(LoggingManagedHttpClientConnection.java:116) - http-outgoing-0 << Content-Length: 2699
2015-01-16 17:33:31,164 [main] DEBUG org.apache.http.impl.auth.HttpAuthenticator(HttpAuthenticator.java:77) - Authentication required
Thanks for any help you can provide.
Regards,
Eric

Answer 1

The error message says quite clearly:
Forefront TMG requires authorization to fulfill the request. Access to the Web Proxy filter is denied.
You need some kind of authorization which you don't provide. This problem is not specific to Apache HTTPClient. Please check with the administrator of the Forefront TMG installation what kind if authorization (and which credentials) you need. It might be the kind of authorization you've tried and only the credentials are wrong or it might be some other kind of authorization required.