Allow setting authenticationEntryPoint for Http Basic

1. Added method authenticationEntryPoint in ServerHttpSecurity to allow
setting authenticationEntryPoint.
2. Added test in ServerHttpSecurityTests to check if
if specified realm name set by authenticationEntryPoint is
returned

Fixes: gh-6270

config/src/main/java/org/springframework/security/config/web/server/ServerHttpSecurity.java

@@ -1878,6 +1878,19 @@ public class ServerHttpSecurity {
 			return this;
 		}
 
+		/**
+		 * Allows easily setting the entry point.
+		 * @param authenticationEntryPoint the {@link ServerAuthenticationEntryPoint} to use
+		 * @return {@link HttpBasicSpec} for additional customization
+		 * @since 5.2.0
+		 * @author Ankur Pathak
+		 */
+		public HttpBasicSpec authenticationEntryPoint(ServerAuthenticationEntryPoint authenticationEntryPoint){
+			Assert.notNull(authenticationEntryPoint, "authenticationEntryPoint cannot be null");
+			this.entryPoint = authenticationEntryPoint;
+			return this;
+		}
+
 		/**
 		 * Allows method chaining to continue configuring the {@link ServerHttpSecurity}
 		 * @return the {@link ServerHttpSecurity} to continue configuring

config/src/test/java/org/springframework/security/config/web/server/ServerHttpSecurityTests.java

@@ -64,6 +64,7 @@ import org.springframework.web.server.WebFilter;
 import org.springframework.security.web.server.context.SecurityContextServerWebExchangeWebFilter;
 import org.springframework.web.server.WebFilterChain;
 import org.springframework.security.web.server.authentication.AnonymousAuthenticationWebFilterTests;
+import org.springframework.security.web.server.authentication.HttpBasicServerAuthenticationEntryPoint;
 
 /**
  * @author Rob Winch
@@ -255,6 +256,29 @@ public class ServerHttpSecurityTests {
 		assertThat(result.getResponseCookies().getFirst("SESSION")).isNull();
 	}
 
+	@Test
+	public void basicWithCustomRealmName() {
+		this.http.securityContextRepository(new WebSessionServerSecurityContextRepository());
+		HttpBasicServerAuthenticationEntryPoint authenticationEntryPoint = new HttpBasicServerAuthenticationEntryPoint();
+		authenticationEntryPoint.setRealm("myrealm");
+		this.http.httpBasic().authenticationEntryPoint(authenticationEntryPoint);
+		this.http.authenticationManager(this.authenticationManager);
+		ServerHttpSecurity.AuthorizeExchangeSpec authorize = this.http.authorizeExchange();
+		authorize.anyExchange().authenticated();
+
+		WebTestClient client = buildClient();
+
+		EntityExchangeResult<String> result = client.get()
+				.uri("/")
+				.exchange()
+				.expectStatus().isUnauthorized()
+				.expectHeader().value(HttpHeaders.WWW_AUTHENTICATE, value -> assertThat(value).contains("myrealm"))
+				.expectBody(String.class)
+				.returnResult();
+
+		assertThat(result.getResponseCookies().getFirst("SESSION")).isNull();
+	}
+
 	private <T extends WebFilter> Optional<T> getWebFilter(SecurityWebFilterChain filterChain, Class<T> filterClass) {
 		return (Optional<T>) filterChain.getWebFilters()
 				.filter(Objects::nonNull)