web/src/main/java/org/springframework/security/web/authentication/preauth/AbstractPreAuthenticatedProcessingFilter.java
private void doAuthenticate(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
		Authentication authResult;

		Object principal = getPreAuthenticatedPrincipal(request);
		Object credentials = getPreAuthenticatedCredentials(request);

		if (principal == null) {
			if (logger.isDebugEnabled()) {
				logger.debug("No pre-authenticated principal found in request");
			}

			return;
		}

		if (logger.isDebugEnabled()) {
			logger.debug("preAuthenticatedPrincipal = " + principal
					+ ", trying to authenticate");
		}

		try {
			PreAuthenticatedAuthenticationToken authRequest = new PreAuthenticatedAuthenticationToken(
					principal, credentials);
			authRequest.setDetails(authenticationDetailsSource.buildDetails(request));
			authResult = authenticationManager.authenticate(authRequest);
			successfulAuthentication(request, response, authResult);
		}
		catch (AuthenticationException failed) {
			unsuccessfulAuthentication(request, response, failed);

			if (!continueFilterChainOnUnsuccessfulAuthentication) {
				throw failed;
			}
		}
	}
private void doAuthenticate(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
		Authentication authResult;

		Object principal = getPreAuthenticatedPrincipal(request);
		Object credentials = getPreAuthenticatedCredentials(request);

		if (principal == null) {
			if (logger.isDebugEnabled()) {
				logger.debug("No pre-authenticated principal found in request");
			}

			return;
		}

		if (logger.isDebugEnabled()) {
			logger.debug("preAuthenticatedPrincipal = " + principal
					+ ", trying to authenticate");
		}

		try {
			PreAuthenticatedAuthenticationToken authRequest = new PreAuthenticatedAuthenticationToken(
					principal, credentials);
			authRequest.setDetails(authenticationDetailsSource.buildDetails(request));
			authResult = authenticationManager.authenticate(authRequest);
			successfulAuthentication(request, response, authResult);
		}
		catch (AuthenticationException failed) {
			unsuccessfulAuthentication(request, response, failed);

			if (!continueFilterChainOnUnsuccessfulAuthentication) {
				throw failed;
			}
		}
	}
Do the actual authentication for a pre-authenticated user.