Preserve Null Claim Values

Prior to this commit ClaimTypeConverter returned the claims with the
original value for all the claims with a null converted value.
The changes allows ClaimTypeConverter to overwrite and return claims
with converted value of null.

Closes gh-10135

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/converter/ClaimTypeConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -56,10 +56,7 @@ public final class ClaimTypeConverter implements Converter<Map<String, Object>,
 		this.claimTypeConverters.forEach((claimName, typeConverter) -> {
 			if (claims.containsKey(claimName)) {
 				Object claim = claims.get(claimName);
-				Object mappedClaim = typeConverter.convert(claim);
-				if (mappedClaim != null) {
-					result.put(claimName, mappedClaim);
-				}
+				result.put(claimName, typeConverter.convert(claim));
 			}
 		});
 		return result;

oauth2/oauth2-core/src/test/java/org/springframework/security/oauth2/core/converter/ClaimTypeConverterTests.java

@@ -62,6 +62,8 @@ public class ClaimTypeConverterTests {
 
 	private static final String JSON_OBJECT_CLAIM = "json-object-claim";
 
+	private static final String NULL_OBJECT_CLAIM = "null-object-claim";
+
 	private ClaimTypeConverter claimTypeConverter;
 
 	@BeforeEach
@@ -77,6 +79,7 @@ public class ClaimTypeConverterTests {
 				TypeDescriptor.collection(List.class, TypeDescriptor.valueOf(String.class)));
 		Converter<Object, ?> mapStringObjectConverter = getConverter(TypeDescriptor.map(Map.class,
 				TypeDescriptor.valueOf(String.class), TypeDescriptor.valueOf(Object.class)));
+		Converter<Object, ?> nullConverter = (value) -> null;
 		Map<String, Converter<Object, ?>> claimTypeConverters = new HashMap<>();
 		claimTypeConverters.put(STRING_CLAIM, stringConverter);
 		claimTypeConverters.put(BOOLEAN_CLAIM, booleanConverter);
@@ -85,6 +88,7 @@ public class ClaimTypeConverterTests {
 		claimTypeConverters.put(COLLECTION_STRING_CLAIM, collectionStringConverter);
 		claimTypeConverters.put(LIST_STRING_CLAIM, listStringConverter);
 		claimTypeConverters.put(MAP_STRING_OBJECT_CLAIM, mapStringObjectConverter);
+		claimTypeConverters.put(NULL_OBJECT_CLAIM, nullConverter);
 		this.claimTypeConverter = new ClaimTypeConverter(claimTypeConverters);
 	}
 
@@ -138,6 +142,7 @@ public class ClaimTypeConverterTests {
 		claims.put(MAP_STRING_OBJECT_CLAIM, mapIntegerObject);
 		claims.put(JSON_ARRAY_CLAIM, jsonArray);
 		claims.put(JSON_OBJECT_CLAIM, jsonObject);
+		claims.put(NULL_OBJECT_CLAIM, instant.toString());
 		claims = this.claimTypeConverter.convert(claims);
 		assertThat(claims.get(STRING_CLAIM)).isEqualTo("true");
 		assertThat(claims.get(BOOLEAN_CLAIM)).isEqualTo(Boolean.TRUE);
@@ -148,6 +153,7 @@ public class ClaimTypeConverterTests {
 		assertThat(claims.get(MAP_STRING_OBJECT_CLAIM)).isEqualTo(mapStringObject);
 		assertThat(claims.get(JSON_ARRAY_CLAIM)).isEqualTo(jsonArrayListString);
 		assertThat(claims.get(JSON_OBJECT_CLAIM)).isEqualTo(jsonObjectMap);
+		assertThat(claims.get(NULL_OBJECT_CLAIM)).isNull();
 	}
 
 	@Test

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

@@ -123,8 +123,18 @@ public class MappedJwtClaimSetConverterTests {
 		assertThat(target.get(JwtClaimNames.SUB)).isEqualTo("1234");
 	}
 
+	// gh-10135
 	@Test
 	public void convertWhenConverterReturnsNullThenClaimIsRemoved() {
+		MappedJwtClaimSetConverter converter = MappedJwtClaimSetConverter
+				.withDefaults(Collections.singletonMap(JwtClaimNames.NBF, (nbfClaimValue) -> null));
+		Map<String, Object> source = Collections.singletonMap(JwtClaimNames.NBF, Instant.now());
+		Map<String, Object> target = converter.convert(source);
+		assertThat(target).doesNotContainKey(JwtClaimNames.NBF);
+	}
+
+	@Test
+	public void convertWhenClaimValueIsNullThenClaimIsRemoved() {
 		MappedJwtClaimSetConverter converter = MappedJwtClaimSetConverter.withDefaults(Collections.emptyMap());
 		Map<String, Object> source = Collections.singletonMap(JwtClaimNames.ISS, null);
 		Map<String, Object> target = converter.convert(source);