Validate Parameter in setPostAuthenticationChecks

The null check in setPostAuthenticationChecks of
AbstractUserDetailsReactiveAuthenticationManager asserted the current
field value, which is initialized to a default and can never be null,
instead of the method parameter. As a result, null was silently
accepted and the next authenticate call failed with a raw
NullPointerException instead of failing fast with a clear message.

Closes gh-19276

Signed-off-by: dae won <eodnjs01477@gmail.com>

core/src/main/java/org/springframework/security/authentication/AbstractUserDetailsReactiveAuthenticationManager.java

@@ -184,7 +184,7 @@ public abstract class AbstractUserDetailsReactiveAuthenticationManager
 	 * @since 5.2
 	 */
 	public void setPostAuthenticationChecks(UserDetailsChecker postAuthenticationChecks) {
-		Assert.notNull(this.postAuthenticationChecks, "postAuthenticationChecks cannot be null");
+		Assert.notNull(postAuthenticationChecks, "postAuthenticationChecks cannot be null");
 		this.postAuthenticationChecks = postAuthenticationChecks;
 	}
 

core/src/test/java/org/springframework/security/authentication/UserDetailsRepositoryReactiveAuthenticationManagerTests.java

@@ -90,6 +90,12 @@ public class UserDetailsRepositoryReactiveAuthenticationManagerTests {
 		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> this.manager.setScheduler(null));
 	}
 
+	@Test
+	public void setPostAuthenticationChecksWhenNullThenIllegalArgumentException() {
+		assertThatExceptionOfType(IllegalArgumentException.class)
+			.isThrownBy(() -> this.manager.setPostAuthenticationChecks(null));
+	}
+
 	@Test
 	public void authenticateWhenCustomSchedulerThenUsed() {
 		given(this.scheduler.schedule(any())).willAnswer((a) -> {