可是有時候瀏覽器會彈出一個登錄驗證的對話框。例如以下圖，這就是使用HTTP基本認證。
以下來看看一看這個認證的工作過程:
第一步: client發送http request 給server,server驗證該用戶是否已經登錄驗證過了，假設沒有的話，
server會返回一個401 Unauthozied給client，而且在Response 的 header "WWW-Authenticate" 中加入信息。
例如以下圖。
第二步:瀏覽器在接受到401 Unauthozied后，會彈出登錄驗證的對話框。用戶輸入username和password后，
瀏覽器用BASE64編碼后。放在Authorization header中發送給server。例如以下圖:
第三步: server將Authorization header中的usernamepassword取出，進行驗證， 假設驗證通過，將依據請求，發送資源給client。
以下來看一個JAVA的演示樣例代碼:
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import sun.misc.BASE64Decoder;
public class HTTPAuthServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
String sessionAuth = (String) request.getSession().getAttribute("auth");
if (sessionAuth != null) {
System.out.println("this is next step");
nextStep(request, response);
} else {
if(!checkHeaderAuth(request, response)){
response.setStatus(401);
response.setHeader("Cache-Control", "no-store");
response.setDateHeader("Expires", 0);
response.setHeader("WWW-authenticate", "Basic Realm=\"test\"");
}
}
}
private boolean checkHeaderAuth(HttpServletRequest request, HttpServletResponse response) throws IOException {
String auth = request.getHeader("Authorization");
System.out.println("auth encoded in base64 is " + getFromBASE64(auth));
if ((auth != null) && (auth.length() > 6)) {
auth = auth.substring(6, auth.length());
String decodedAuth = getFromBASE64(auth);
System.out.println("auth decoded from base64 is " + decodedAuth);
request.getSession().setAttribute("auth", decodedAuth);
return true;
}else{
return false;
}
}
private String getFromBASE64(String s) {
if (s == null)
return null;
BASE64Decoder decoder = new BASE64Decoder();
try {
byte[] b = decoder.decodeBuffer(s);
return new String(b);
} catch (Exception e) {
return null;
}
}
public void nextStep(HttpServletRequest request, HttpServletResponse response) throws IOException {
PrintWriter pw = response.getWriter();
pw.println("<html> next step, authentication is : " + request.getSession().getAttribute("auth") + "<br>");
pw.println("<br></html>");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
doGet(request, response);
}
}
當request第一次到達server時。server沒有認證的信息，server會返回一個401 Unauthozied給client。
認證之后將認證信息放在session，以后在session有效期內就不用再認證了。