Polish to Avoid NPE

Issue gh-5648

Co-authored-by: MattyA <mat.auburn@gmail.com>

oauth2/oauth2-jose/src/main/java/org/springframework/security/oauth2/jwt/NimbusJwtDecoder.java

@@ -22,6 +22,7 @@ import java.net.URL;
 import java.security.interfaces.RSAPublicKey;
 import java.text.ParseException;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -54,11 +55,13 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
+import org.springframework.security.oauth2.core.OAuth2Error;
 import org.springframework.security.oauth2.core.OAuth2TokenValidator;
 import org.springframework.security.oauth2.core.OAuth2TokenValidatorResult;
 import org.springframework.security.oauth2.jose.jws.MacAlgorithm;
 import org.springframework.security.oauth2.jose.jws.SignatureAlgorithm;
 import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 import org.springframework.web.client.RestOperations;
 import org.springframework.web.client.RestTemplate;
 
@@ -164,9 +167,17 @@ public final class NimbusJwtDecoder implements JwtDecoder {
 	private Jwt validateJwt(Jwt jwt){
 		OAuth2TokenValidatorResult result = this.jwtValidator.validate(jwt);
 		if (result.hasErrors()) {
-			String description = result.getErrors().iterator().next().getDescription();
+			Collection<OAuth2Error> errors = result.getErrors();
+			String validationErrorString = "Unable to validate Jwt";
+			for (OAuth2Error oAuth2Error : errors) {
+				if (!StringUtils.isEmpty(oAuth2Error.getDescription())) {
+					validationErrorString = String.format(
+							DECODING_ERROR_MESSAGE_TEMPLATE, oAuth2Error.getDescription());
+					break;
+				}
+			}
 			throw new JwtValidationException(
-					String.format(DECODING_ERROR_MESSAGE_TEMPLATE, description),
+					validationErrorString,
 					result.getErrors());
 		}
 

oauth2/oauth2-jose/src/main/java/org/springframework/security/oauth2/jwt/NimbusReactiveJwtDecoder.java

@@ -16,6 +16,7 @@
 package org.springframework.security.oauth2.jwt;
 
 import java.security.interfaces.RSAPublicKey;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -51,12 +52,14 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.convert.converter.Converter;
+import org.springframework.security.oauth2.core.OAuth2Error;
 import org.springframework.security.oauth2.core.OAuth2TokenValidator;
 import org.springframework.security.oauth2.core.OAuth2TokenValidatorResult;
 import org.springframework.security.oauth2.jose.jws.JwsAlgorithm;
 import org.springframework.security.oauth2.jose.jws.MacAlgorithm;
 import org.springframework.security.oauth2.jose.jws.SignatureAlgorithm;
 import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 import org.springframework.web.reactive.function.client.WebClient;
 
 /**
@@ -172,10 +175,16 @@ public final class NimbusReactiveJwtDecoder implements ReactiveJwtDecoder {
 
 	private Jwt validateJwt(Jwt jwt) {
 		OAuth2TokenValidatorResult result = this.jwtValidator.validate(jwt);
-
-		if ( result.hasErrors() ) {
-			String message = result.getErrors().iterator().next().getDescription();
-			throw new JwtValidationException(message, result.getErrors());
+		if (result.hasErrors()) {
+			Collection<OAuth2Error> errors = result.getErrors();
+			String validationErrorString = "Unable to validate Jwt";
+			for (OAuth2Error oAuth2Error : errors) {
+				if (!StringUtils.isEmpty(oAuth2Error.getDescription())) {
+					validationErrorString = oAuth2Error.getDescription();
+					break;
+				}
+			}
+			throw new JwtValidationException(validationErrorString, errors);
 		}
 
 		return jwt;

oauth2/oauth2-jose/src/test/java/org/springframework/security/oauth2/jwt/NimbusJwtDecoderTests.java

@@ -193,6 +193,22 @@ public class NimbusJwtDecoderTests {
 				.hasFieldOrPropertyWithValue("errors", Arrays.asList(firstFailure, secondFailure));
 	}
 
+	@Test
+	public void decodeWhenReadingErrorPickTheFirstErrorMessage() {
+		OAuth2TokenValidator<Jwt> jwtValidator = mock(OAuth2TokenValidator.class);
+		this.jwtDecoder.setJwtValidator(jwtValidator);
+
+		OAuth2Error errorEmpty = new OAuth2Error("mock-error", "", "mock-uri");
+		OAuth2Error error = new OAuth2Error("mock-error", "mock-description", "mock-uri");
+		OAuth2Error error2 = new OAuth2Error("mock-error-second", "mock-description-second", "mock-uri-second");
+		OAuth2TokenValidatorResult result = OAuth2TokenValidatorResult.failure(errorEmpty, error, error2);
+		when(jwtValidator.validate(any(Jwt.class))).thenReturn(result);
+
+		Assertions.assertThatCode(() -> this.jwtDecoder.decode(SIGNED_JWT))
+				.isInstanceOf(JwtValidationException.class)
+				.hasMessageContaining("mock-description");
+	}
+
 	@Test
 	public void decodeWhenUsingSignedJwtThenReturnsClaimsGivenByClaimSetConverter() {
 		Converter<Map<String, Object>, Map<String, Object>> claimSetConverter = mock(Converter.class);

oauth2/oauth2-jose/src/test/java/org/springframework/security/oauth2/jwt/NimbusReactiveJwtDecoderTests.java

@@ -221,6 +221,22 @@ public class NimbusReactiveJwtDecoderTests {
 				.hasMessageContaining("mock-description");
 	}
 
+	@Test
+	public void decodeWhenReadingErrorPickTheFirstErrorMessage() {
+		OAuth2TokenValidator<Jwt> jwtValidator = mock(OAuth2TokenValidator.class);
+		this.decoder.setJwtValidator(jwtValidator);
+
+		OAuth2Error errorEmpty = new OAuth2Error("mock-error", "", "mock-uri");
+		OAuth2Error error = new OAuth2Error("mock-error", "mock-description", "mock-uri");
+		OAuth2Error error2 = new OAuth2Error("mock-error-second", "mock-description-second", "mock-uri-second");
+		OAuth2TokenValidatorResult result = OAuth2TokenValidatorResult.failure(errorEmpty, error, error2);
+		when(jwtValidator.validate(any(Jwt.class))).thenReturn(result);
+
+		assertThatCode(() -> this.decoder.decode(this.messageReadToken).block())
+				.isInstanceOf(JwtValidationException.class)
+				.hasMessageContaining("mock-description");
+	}
+
 	@Test
 	public void decodeWhenUsingSignedJwtThenReturnsClaimsGivenByClaimSetConverter() {
 		Converter<Map<String, Object>, Map<String, Object>> claimSetConverter = mock(Converter.class);