Explain the flow of google auth in spring boot

@Bean
    public SecurityFilterChain googleOAuth2SecurityFilterChain(HttpSecurity httpSecurity) throws Exception {
        return httpSecurity
                .securityMatcher(new AntPathRequestMatcher("/oauth2/**"))
                .csrf(AbstractHttpConfigurer::disable)
                .authorizeHttpRequests(auth -> auth
                        .requestMatchers("/auth/login/**", "/oauth2/**", "/login/oauth2/**", "/login").permitAll()
                        .anyRequest().authenticated()
                )
                .oauth2Login(oauth2 -> oauth2
                        .loginPage("/auth/login/google")
                        .defaultSuccessUrl("/dashboard", true)
                        .failureUrl("/login?error=true")
                        .userInfoEndpoint(userInfo -> userInfo.userService(googleOAuth2Service))
                        .successHandler((request, response, authentication) -> {
                            DefaultOAuth2User oauth2User = (DefaultOAuth2User) authentication.getPrincipal();
                            String token = oauth2User.getAttribute("token");
                            response.addHeader(HttpHeaders.AUTHORIZATION, "Bearer " + token);
                        })
                )
                .exceptionHandling(ex -> ex
                        .authenticationEntryPoint(new CustomOAuth2AuthenticationEntryPoint())
                        .accessDeniedHandler(new CustomAccessDeniedHandler())
                )
                .logout(logout -> logout
                        .logoutUrl("/logout")
                        .logoutSuccessUrl("/login?logout=true")
                        .addLogoutHandler(logoutHandlerService)
                )
                .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
                .build();
    }

@Bean
    public SecurityFilterChain googleOAuth2SecurityFilterChain(HttpSecurity httpSecurity) throws Exception {
        return httpSecurity
                .securityMatcher(new AntPathRequestMatcher("/oauth2/**"))
                .csrf(AbstractHttpConfigurer::disable)
                .authorizeHttpRequests(auth -> auth
                        .requestMatchers("/auth/login/**", "/oauth2/**", "/login/oauth2/**", "/login").permitAll()
                        .anyRequest().authenticated()
                )
                .oauth2Login(oauth2 -> oauth2
                        .loginPage("/auth/login/google")
                        .defaultSuccessUrl("/dashboard", true)
                        .failureUrl("/login?error=true")
                        .userInfoEndpoint(userInfo -> userInfo.userService(googleOAuth2Service))
                        .successHandler((request, response, authentication) -> {
                            DefaultOAuth2User oauth2User = (DefaultOAuth2User) authentication.getPrincipal();
                            String token = oauth2User.getAttribute("token");
                            response.addHeader(HttpHeaders.AUTHORIZATION, "Bearer " + token);
                        })
                )
                .exceptionHandling(ex -> ex
                        .authenticationEntryPoint(new CustomOAuth2AuthenticationEntryPoint())
                        .accessDeniedHandler(new CustomAccessDeniedHandler())
                )
                .logout(logout -> logout
                        .logoutUrl("/logout")
                        .logoutSuccessUrl("/login?logout=true")
                        .addLogoutHandler(logoutHandlerService)
                )
                .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
                .build();
    }