Mark GrantedAuthority#getAuthority as @Nullable

Closes: gh-17999

Signed-off-by: Andrey Litvitski <andrey1010102008@gmail.com>

core/src/main/java/org/springframework/security/authorization/AllRequiredFactorsAuthorizationManager.java

@@ -99,7 +99,7 @@ public final class AllRequiredFactorsAuthorizationManager<T> implements Authoriz
 	private @Nullable RequiredFactorError requiredFactorError(RequiredFactor requiredFactor,
 			List<GrantedAuthority> currentFactors) {
 		Optional<GrantedAuthority> matchingAuthority = currentFactors.stream()
-			.filter((authority) -> authority.getAuthority().equals(requiredFactor.getAuthority()))
+			.filter((authority) -> Objects.equals(authority.getAuthority(), requiredFactor.getAuthority()))
 			.findFirst();
 		if (!matchingAuthority.isPresent()) {
 			return RequiredFactorError.createMissing(requiredFactor);

core/src/main/java/org/springframework/security/authorization/AuthorityReactiveAuthorizationManager.java

@@ -17,6 +17,7 @@
 package org.springframework.security.authorization;
 
 import java.util.List;
+import java.util.Objects;
 
 import reactor.core.publisher.Mono;
 
@@ -47,8 +48,8 @@ public class AuthorityReactiveAuthorizationManager<T> implements ReactiveAuthori
 		// @formatter:off
 		return authentication.filter(Authentication::isAuthenticated)
 				.flatMapIterable(Authentication::getAuthorities)
-				.map(GrantedAuthority::getAuthority)
-				.any((grantedAuthority) -> this.authorities.stream().anyMatch((authority) -> authority.getAuthority().equals(grantedAuthority)))
+				.mapNotNull(GrantedAuthority::getAuthority)
+				.any((grantedAuthority) -> this.authorities.stream().anyMatch((authority) -> Objects.equals(authority.getAuthority(), grantedAuthority)))
 				.map((granted) -> ((AuthorizationResult) new AuthorityAuthorizationDecision(granted, this.authorities)))
 				.defaultIfEmpty(new AuthorityAuthorizationDecision(false, this.authorities));
 		// @formatter:on

core/src/main/java/org/springframework/security/core/GrantedAuthority.java

@@ -18,6 +18,8 @@ package org.springframework.security.core;
 
 import java.io.Serializable;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.security.authorization.AuthorizationManager;
 
 /**
@@ -46,6 +48,6 @@ public interface GrantedAuthority extends Serializable {
 	 * granted authority cannot be expressed as a <code>String</code> with sufficient
 	 * precision).
 	 */
-	String getAuthority();
+	@Nullable String getAuthority();
 
 }

core/src/main/java/org/springframework/security/core/authority/mapping/SimpleAuthorityMapper.java

@@ -64,7 +64,10 @@ public final class SimpleAuthorityMapper implements GrantedAuthoritiesMapper, In
 	public Set<GrantedAuthority> mapAuthorities(Collection<? extends GrantedAuthority> authorities) {
 		HashSet<GrantedAuthority> mapped = new HashSet<>(authorities.size());
 		for (GrantedAuthority authority : authorities) {
-			mapped.add(mapAuthority(authority.getAuthority()));
+			String authorityStr = authority.getAuthority();
+			if (authorityStr != null) {
+				mapped.add(mapAuthority(authorityStr));
+			}
 		}
 		if (this.defaultAuthority != null) {
 			mapped.add(this.defaultAuthority);