HTTPClient sends out two requests when using Basic Auth?

问题

I have been using HTTPClient version 4.1.2 to try to access a REST over HTTP API that requires Basic Authentication. Here is client code:

DefaultHttpClient httpClient = new DefaultHttpClient(new ThreadSafeClientConnManager());
// Enable HTTP Basic Auth
httpClient.getCredentialsProvider().setCredentials(
    new AuthScope(AuthScope.ANY_HOST, AuthScope.ANY_PORT), 
    new UsernamePasswordCredentials(this.username, this.password));

HttpHost proxy = new HttpHost(this.proxyURI.getHost(), this.proxyURI.getPort());

httpClient.getParams().setParameter(ConnRouteParams.DEFAULT_PROXY, proxy);

When I construct a POST request, like this:

HttpPost request = new HttpPost("http://my/url");
request.addHeader(new BasicHeader("Content-type", "application/atom+xml; type=entry")); // required by vendor
request.setEntity(new StringEntity("My content"));

HttpResponse response = client.execute(request);

I see in Charles Proxy that there are two requests being sent. One without the Authorization: Basic ... header and one with it. The first one fails with a 401, as you would expect, but the second goes through just fine with a 201.

Does anyone know why this happens? Thanks!

EDIT:

I should make clear that I have already looked at this question, but as you can see I set the AuthScope the same way and it didn't solve my problem. Also, I am creating a new HttpClient every time I made a request (though I use the same ConnectionManager), but even if I use the same HttpClient for multiple requests, the problem still persists.

EDIT 2:

So it looks like what @LastCoder was suggesting is the way to do. See this answer to another question. The problem stems from my lack of knowledge around the HTTP spec. What I'm looking to do is called "preemptive authentication" and the HttpClient docs mention it here. Thankfully, the answer linked to above is a much shorter and cleaner way to do it.

回答1:

Rather than using .setCredentials() why don't you just encode USERNAME:PASSWORD and add the authentication header with .addHeader()

回答2:

This means that your server/target endpoint is creating a new session for every client request. This forces every request of yours to go through a hand-shake, which means the clients first makes the call and realizes that it needs authorization, then it follows with the authorization. What you need to do is send the authorization preemptively as follows:

httpClient.getParams().setAuthenticationPreemptive(true);

Just to understand the process you may log your client request headers, to give you an idea of what your client is sending and receiving: See if this works.

来源：https://stackoverflow.com/questions/9539141/httpclient-sends-out-two-requests-when-using-basic-auth