public Authentication attemptAuthentication(HttpServletRequest request,
            HttpServletResponse response) throws AuthenticationException {
        if (postOnly && !request.getMethod().equals("POST")) {
            throw new AuthenticationServiceException(
                    "Authentication method not supported: " + request.getMethod());
        }
        String username = obtainUsername(request);
        String password = obtainPassword(request);
        if (username == null) {
            username = "";
        }
        if (password == null) {
            password = "";
        }
        username = username.trim();
        UsernamePasswordAuthenticationToken authRequest = new UsernamePasswordAuthenticationToken(
                username, password);
        // Allow subclasses to set the "details" property
        setDetails(request, authRequest);
        return this.getAuthenticationManager().authenticate(authRequest);
    }

 1 public Authentication authenticate(Authentication authentication)
 2             throws AuthenticationException {
 3         Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,
 4                 messages.getMessage(
 5                         "AbstractUserDetailsAuthenticationProvider.onlySupports",
 6                         "Only UsernamePasswordAuthenticationToken is supported"));
 7 
 8         // Determine username
 9         String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
10                 : authentication.getName();
11 
12         boolean cacheWasUsed = true;
13         UserDetails user = this.userCache.getUserFromCache(username);
14 
15         if (user == null) {
16             cacheWasUsed = false;
17 
18             try {
19                 user = retrieveUser(username,
20                         (UsernamePasswordAuthenticationToken) authentication);
21             }
22             catch (UsernameNotFoundException notFound) {
23                 logger.debug("User \'" + username + "\' not found");
24 
25                 if (hideUserNotFoundExceptions) {
26                     throw new BadCredentialsException(messages.getMessage(
27                             "AbstractUserDetailsAuthenticationProvider.badCredentials",
28                             "Bad credentials"));
29                 }
30                 else {
31                     throw notFound;
32                 }
33             }
34 
35             Assert.notNull(user,
36                     "retrieveUser returned null - a violation of the interface contract");
37         }
38 
39         try {
40             preAuthenticationChecks.check(user);
41             additionalAuthenticationChecks(user,
42                     (UsernamePasswordAuthenticationToken) authentication);
43         }
44         catch (AuthenticationException exception) {
45             if (cacheWasUsed) {
46                 // There was a problem, so try again after checking
47                 // we\'re using latest data (i.e. not from the cache)
48                 cacheWasUsed = false;
49                 user = retrieveUser(username,
50                         (UsernamePasswordAuthenticationToken) authentication);
51                 preAuthenticationChecks.check(user);
52                 additionalAuthenticationChecks(user,
53                         (UsernamePasswordAuthenticationToken) authentication);
54             }
55             else {
56                 throw exception;
57             }
58         }
59 
60         postAuthenticationChecks.check(user);
61 
62         if (!cacheWasUsed) {
63             this.userCache.putUserInCache(user);
64         }
65 
66         Object principalToReturn = user;
67 
68         if (forcePrincipalAsString) {
69             principalToReturn = user.getUsername();
70         }
71 
72         return createSuccessAuthentication(principalToReturn, authentication, user);
73     }