How-to: Authenticate using a Single Page Application with PKCE

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.annotation.Order;
import org.springframework.http.MediaType;
import org.springframework.security.config.Customizer;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.oauth2.server.authorization.config.annotation.web.configuration.OAuth2AuthorizationServerConfiguration;
import org.springframework.security.oauth2.server.authorization.config.annotation.web.configurers.OAuth2AuthorizationServerConfigurer;
import org.springframework.security.web.SecurityFilterChain;
import org.springframework.security.web.authentication.LoginUrlAuthenticationEntryPoint;
import org.springframework.security.web.util.matcher.MediaTypeRequestMatcher;
import org.springframework.web.cors.CorsConfiguration;
import org.springframework.web.cors.CorsConfigurationSource;
import org.springframework.web.cors.UrlBasedCorsConfigurationSource;

@Configuration
@EnableWebSecurity
public class SecurityConfig {

	@Bean
	@Order(1)
	public SecurityFilterChain authorizationServerSecurityFilterChain(HttpSecurity http)
			throws Exception {
		OAuth2AuthorizationServerConfiguration.applyDefaultSecurity(http);
		http.getConfigurer(OAuth2AuthorizationServerConfigurer.class)
			.oidc(Customizer.withDefaults());	// Enable OpenID Connect 1.0
		http
			// Redirect to the login page when not authenticated from the
			// authorization endpoint
			.exceptionHandling((exceptions) -> exceptions
				.defaultAuthenticationEntryPointFor(
					new LoginUrlAuthenticationEntryPoint("/login"),
					new MediaTypeRequestMatcher(MediaType.TEXT_HTML)
				)
			)
			// Accept access tokens for User Info and/or Client Registration
			.oauth2ResourceServer((oauth2) -> oauth2.jwt(Customizer.withDefaults()));

		return http.cors(Customizer.withDefaults()).build();
	}

	@Bean
	@Order(2)
	public SecurityFilterChain defaultSecurityFilterChain(HttpSecurity http)
			throws Exception {
		http
			.authorizeHttpRequests((authorize) -> authorize
				.anyRequest().authenticated()
			)
			// Form login handles the redirect to the login page from the
			// authorization server filter chain
			.formLogin(Customizer.withDefaults());

		return http.cors(Customizer.withDefaults()).build();
	}

	@Bean
	public CorsConfigurationSource corsConfigurationSource() {
		UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
		CorsConfiguration config = new CorsConfiguration();
		config.addAllowedHeader("*");
		config.addAllowedMethod("*");
		config.addAllowedOrigin("http://127.0.0.1:4200");
		config.setAllowCredentials(true);
		source.registerCorsConfiguration("/**", config);
		return source;
	}

}